FIG. 1. Construction of Peck's Run Sewer, Baltimore, Maryland. Frontispiece. SEWERAGE* *** AND SEWAGE TREATMENT BY HAROLD E. BABBITT, M.S. Assistant Professor, Municipal and Sanitary Engineering, University of Illinois; Associate Member American Society of Civil Engineers NEW YORK JOHN WILEY & SONS, INC. LONDON: CHAPMAN & HALL, LIMITED 1922 Copyright, 1922, by HAROLD E. BABBITT, M.S. PRESS OF BRAUNWOHTH IL CO. BOOK MANUFACTURERS BROOKLYN. N. Y. PREFACE THIS book is a development of class-room and lecture notes prepared by the author for use in his classes at the University of Illinois. He has found such notes necessary, since among the many books dealing with sewerage and sewage treatment he has found none suitable as a text-book designed to cover the entire subject. The need for a single book of the character described has been expressed by engineers in practice, and by students and teachers for use in the class-room. This book has been prepared to meet both these needs. It is hoped that the searching questions propounded by students in using the original notes, and the suggestions and criticisms of engineers and teachers who have read the manuscript, have resulted in a text which can be readily understood. The ground covered includes an exposition of the princ : ples and methods for the designing, construction and maintenance of sewerage works, and also of the treatment of sewage. In covering so wide a field the author has deemed it necessary to include some chapters which might equally well appear in works on other branches of engineering, such as the chapter on Pumps and Pumping Stations. Special stress has been laid on che funda- mentals of the subject rather than the details of practice, although illustrations have been drawn freely from practical work. The quotation of expert opinions which may be in controversy, or the citation of examples of different methods of accomplishing the same thing, has been avoided when possible in order to simplify explanations and to avoid confusing the beginner. The work is to some extent a compilation of notes and quota- tions which have been collected by the author during years of study and teaching the subject. Credit has been given wherever due, and at the same time references have pointed out the original sources whenever possible. These references, which 481200 vi PREFACE have been supplemented by brief bibliographies at the end of certain chapters, will be useful to the student and engineer inter- ested in further study. Occasionally the original reference has been lost or the phraseology of a quotation has been so altered by class-room use, as to make it impossible to trace the original source, so that in some few instances full credit may be lacking. The author is indebted to many of his friends for their criti- cisms and suggestions in the preparation of the manuscript; but he desires particularly to acknowledge the assistance of Professor A. N. Talbot, Professor of Municipal and Sanitary Engineering at the University of Illinois, and of Professor M. L. Enger, Professor of Mechanics and Hydraulics at the University of Illinois, in the entire work; also that of Mr. T. D. Pitts, Prin- cipal Assistant Engineer of the Baltimore Sewerage Commis- sion during the construction of the Baltimore sewers, for his suggestions on the first half of the book; and to Mr. Paul Hansen, consulting engineer, of Chicago, and to Mr. Langdon Pearse, Sanitary Engineer of the Sanitary District of Chicago, for their help on the section covering the treatment of sewage; and to Professor Edward Bartow, Professor of Chemistry at the University of Iowa, for his review of the chapter on Activated Sludge; in general his thanks are due to all others who have furnished suggestions, illustrations, or quotations, acknowledg- ments of which have been included in the text. H. E. B. URBANA, ILLINOIS, 1922. TABLE OF CONTENTS CHAPTER I INTRODUCTION PAGES 1. Sewerage and the Sanitary Engineer. 2. Historical. 3. Methods of Collection. 4. Methods of Disposal. 5. Methods of Treat- ment. 6. Definitions 1-8 CHAPTER II WORK PRELIMINARY TO DESIGN 7. Division of Work. 8. Preliminary. 9. Estimate of cost. METH- ODS OF FINANCING. 10. Bond Issues. 11. Special Assessment. 12. General Taxation. 13. Private Capital. PRELIMINARY WORK. 14. Preparing for Design. 15. Underground Surveys. 16, Borings 9-23 CHAPTER III QUANTITY OF SEWAGE 17. Dry Weather Flow. 18. Methods for Predicting Population. 19. Extent of Prediction. 20. Sources of Information on Population. 21. Density of Population. 22. Changes in Area. 23. Relation between Population and Sewage Flow. 24. Char- acter of District. 25. Fluctuations in Rate of Sewage Flow. 26. Effect of Ground Water. 27. Resume of Method for Determination of Quantity of Dry-weather Sewage. QUANTITY OF STORM WATER. 28. The Rational Method. 29. Rate of Rainfall. 30. Time of Concentration. 31. Character of Sur- face. 32. Empirical Formulas. 33. Extent and Intensity of Storms 24-50 vii viii CONTENTS CHAPTER IV HYDRAULICS OF SEWERS PAGES 34. Principles. 35. Formulas. 36. Solution of Formulas. 37. Use of Diagrams. 38. Flow in Circular Pipes Partly Full. 39. Sec- tions Other than Circular. 40. Non-Uniform Flow 51-77 CHAPTER V DESIGN OF SEWERAGE SYSTEMS 41. The Plan. 42. Preliminary Map. 43. Layout of the Separate System. 44. Location and Numbering of Manholes. 45. Drainage Areas. 46. Quantity of Sewage. 47. Surface Profile. 48. Slope and Diameter of Sewers. 49. The Sewer Profile. DESIGN OF A STORM-WATER SEWER SYSTEM. 50. Planning the System. 51. Location of Street Inlets. 52. Drainage Areas. 53. Computation of Flood Flow by Me Math Formula. 54. Computation of Flood Flow by Rational Method 78-98 CHAPTER VI APPURTENANCES 55. General. 56. Manholes. 57. Lampholes. 58. Street Inlets. 59. Catch-basins. 60. Grease Traps. 61. Flush-tanks. 62. Siphons. 63. Regulators. 64. Junctions. 65. Outlets. 66. Foundations. 67. Underdrains. . 99-126 CHAPTER VII PUMPS AND PUMPING STATIONS 68. Need. 69. Reliability. 70. Equipment. 71. The Building. 72. Capacity of Pumps. 73 Capacity of Receiving Well. 74. Types of Pumping Machinery. 75. Sizes and Descriptions of Pumps. 76. Definitions of Duties and Efficiency. 77. Details of Centrifugal Pumps. 78. Centrifugal Pump Characteristics. 79. Setting of Centrifugal Pumps. 80. Steam Pumps and Pumping Engines. 81. Steam Turbines. 82. Steam Boilers. 83. Air Ejectors. 84. Electric Motors. 85. Internal Com- CONTENTS ix PAGES bustion Engines. 86. Selection of Pumping Machinery. 87. Costs of Pumping Machinery. 88. Cost Comparisons of Dif- ferent Designs. 89. Number and Capacity of Pumping Units. 127-163 CHAPTER VIII MATERIALS FOR SEWERS 90. Materials. 91. Vitrified Clay Pipe. 92. Cement and Concrete Pipe. 93. Proportioning of Concrete. 94. Waterproofing of Concrete. 95. Mixing and Placing Concrete. 96. Sewer Brick. 97. Vitrified Clay Sewer Block. 98. Cast Iron, Steel, and Wood. 164-193 CHAPTER IX DESIGN OF THE SEWER RING 99. Stresses in Buried Pipe. 100. Design of Steel Pipe. 101. Design of Wood Stave Pipe. 102. External Loads on Buried Pipe. 103. Stresses in Circular Ring. 104. Analysis of Sewer Arches. 105. Reinforced Concrete Sewer Design 194-210 CHAPTER X CONTRACTS AND SPECIFICATIONS 106. Importance of the Subject. 107. Scope of the Subject. 108. Types of Contracts. 109. The Agreement. 110. The Advertise- ment. 111. Information and Instructions for Bidders. 112. Proposal. 113. General Specifications. 114. Technical Specifi- cations. 115. Special Specifications. 116. The Contract. 117. The Bond 211-232 CHAPTER XI CONSTRUCTION 118. Elements. WORK OF THE ENGINEER. 119. Duties. 120. Inspection. 121. Interpretation of Contract. 122. Unex- pected Situations. 123. Cost Data and Estimates. 124. Progress Reports. 125. Records. EXCAVATION. 126. Speci- fications. 127. Hand Excavation. 128. Machine Excavation. X CONTENTS PAGES 129. Types of Machines. 130. Continuous Bucket Exca- vators. 131. Cableway and Trestle Excavators. 132. Tower Cableways. 133. Steam Shovels. 134. Drag Line and Bucket Excavators. 135. Excavation in Quicksand. 136. Pumping and Drainage. 137. Trench Pump. 138. Diaphragm Pump. 139. Jet Pump. 140. Steam Vacuum Pumps. 141. Centrif- ugal and Reciprocating Pumps. 142. Well Points. 143. Rock Excavation. 144. Power Drilling. 145. Steam or Air for Power. 146. Depth of Drill Hole. 147. Diameter of Drill Hole. 148. Spacing of Drill Holes. SHEETING AND BRACING. 149. Purposes and Types. 150. Stay Bracing. 151. Skeleton Sheeting. 152. Poling Boards. 153. Box Sheeting. 154. Vertical Sheeting. 155. Pulling Wood Sheeting. 156. Earth Pressures. 157. Design of Sheeting and Bracing. 158. Steel Sheet Piling. LINE AND GRADE. 159. Locating the Trench. 160. Final Line and Grade. 161. Transferring Grade and Line to the Pipe. 162. Line and Grade in Tunnel. TUN- NELLING. 163. Depth. 164. Shafts. 165. Timbering. 166. Shields. 167. Tunnel Machines. 168. Rock Tunnels. 169. Ventilation. 170. Compressed Air. EXPLOSIVES AND BLASTING. 171. Requirements. 172. Types of Explosives. 173. Per- missible Explosives. 174. Strength. 175. Fuses and Deto- nators. 176. Care in Handling. 177. Priming. Loading, and Firing. 178. Quantity of Explosive. PIPE SEWERS. 179. The Trench Bottom. 180. Laying Pipe. 181. Joints. 182. Labor and Progress. BRICK AND BLOCK SEWERS. 183. The Invert. 184. The Arch. 185. Block Sewers. 186. Organization. 187. Rate of Progress. CONCRETE SEWERS. 188. Construction in Open Cut. 189. Construction in Tunnels. 190. Materials for Forms. 191. Design of Forms. 192. Wooden Forms. 193. Steel-lined Wooden Forms. 194. Steel Forms. 195. Rein- forcement. 196. Cost of Concrete Sewers. BACKFILLING. 197. Method 233-331 CHAPTER XII MAINTENANCE OF SEWERS 198. Work Involved. 199. Causes of Troubles. 200. Inspection. 201. Repairs. 202. Cleaning of Sewers. 203. Flushing Sewers. 204. Cleaning Catch-basins. 205. Protection of Sewers. 206. Explosions in Sewers, 207. Valuation of Sewers 332-351 CHAPTER XIII COMPOSITION AND PROPERTIES OF SEWAGE 208. Physical Characteristics. 209. Chemical Composition. 210. Significance of Chemical Constituents. 211. Sewage Bacteria. CONTENTS xi PAGES 212. Organic Life in Sewage. 213. Decomposition of Sewage. 214. The Nitrogen Cycle. 215. Plankton and Macroscopic Organisms. 216. Variations in the Quality of Sewage. 217. Sewage Disposal. 218. Methods of Sewage Treatment 352-371 CHAPTER XIV DISPOSAL BY DILUTION 219. Definition. 220. Conditions Required for Success. 221. Self- purification of Running Streams. 222. Self-purification of Lakes. 223. Dilution in Salt Water. 224. Quantity of Diluting Water Needed. 225. Governmental Control. 226. Prelimi- nary Treatment. 227. Preliminary Investigations 372-382 CHAPTER XV SCREENING AND SEDIMENTATION 228. Purpose. 229. Types of Screens. 230. Sizes of Openings. 231. Design of Fixed and Movable Screens. PLAIN SEDIMEN- TATION. 232. Theory of Sedimentation. 233. Types of Sedi- mentation Basins. 234. Limiting Velocities. 235. Quantity and Character of Grit. 236. Dimensions of Grit Chambers. 237. Existing Grit Chambers. 238. Number of Grit Chambers. 239. Quantity and Characteristics of Sludge from Plain Sedi- mentation. 240. Dimensions of Sedimentation Basins. CHEM- ICAL PRECIPITATION. 241. The Process. 242. Chemicals. 243. Preparation and Addition of Chemicals. 244. Results. . . . 383-409 CHAPTER XVI SEPTICIZATION 245. The Process. 246. The Septic Tank. 247. Results of Septic Action. 248. Design of Septic Tanks. 249. ImhorT Tanks. 250. Design of ImhorT Tanks. 251. Imhoff Tank Results. 252. Status of Imhoff Tanks. 253. Operation of ImhorT Tanks. 254. Other Tanks 410-430 CHAPTER XVII FILTRATION AND IRRIGATION 255. Theory. 256. The Contact Bed. 257. The Trickling Filter. 258. Intermittent Sand Filter. 259. Cost of Filtration. IRRI- GATION. 260. The Process. 261. Status. 262. Preparation and Operation. 263. Sanitary Aspects. 264. The Crop 431-464 xii CONTENTS CHAPTER XVIII ACTIVATED SLUDGE PAGES 265. The Process. 266. Composition. 267. Advantages and Disadvantages. 268. Historical. 269. Aeration Tank. 270. Sedimentation Tank. 271. Reaeration Tank. 272. Air Dis- tribution. 273. Obtaining Activated Sludge. 274. Cost 465-479 CHAPTER XIX ACID PRECIPITATION, LIME AND ELECTRICITY, AND DISINFECTION 275. The Miles Acid Process. ELECTROLYTIC TREATMENT. 276. The Process. DISINFECTION. 277. Disinfection of Sewage. . . . 482-493 CHAPTER XX SLUDGE 278. Methods of Disposal. 279. Lagooning. 280. Dilution. 281. Burial. 282. Drying 495-505 CHAPTER XXI AUTOMATIC DOSING DEVICES 283. Types." 1 284. Operation. 285. Three Alternating Siphons. 286. Four or More Alternating Siphons. 287. Timed Siphons. 288. Multiple Alternating and Timed Siphons 506-512 SEWERAGE AND SEWAGE TREATMENT CHAPTER I INTRODUCTION 1. Sewerage and the Sanitary Engineer. Present day concep- tions of sanitation are based on the scientific discoveries which have resulted so much in the increased comfort and safety of human life during the past century, in the increase of our material possessions, and the extent of our knowledge. The danger to health in the accumulation of filth, the spreading of disease by various agents, the germ theory of disease, and other important principles of sanitation can be counted among the more recent scientific discoveries and pronouncements. Experience has shown, and continues to show, that the increase of population may be inhibited by accumulations of human waste in populous districts. The removal of these wastes is therefore essential to the existence of our modern cities. The greatest need of a modern city is its water supply. With- out it city life would be impossible. The next most important need is the removal of waste matters, particularly wastes con- taining human excreta or the germs of disease. To exist without street lights, pavements, street cars, telephones, and the many other attributes of modern city life might be possible, although uncomfortable. To exist in a large city without either water or sewerage would be impossible. The service rendered by the sani- tary engineer to the large municipality is indispensable. In addition to the service necessary to the maintenance of life in large cities, the sanitary engineer serves the smaller city, the rural community, the isolated institution, and the private estate with sanitary conveniences which make possible comfortable 2 INTRODUCTION existence in them, and which are frequently considered as of paramount necessity. Training for service in municipal sanita- tion is training for a service which has a more direct beneficial effect on humanity than any other engineering work, or any other profession. W. P. Gerhard states: A Sanitary Engineer is an engineer who carries out those works of civil engineering which have for their object: (a) The promotion of the public and individual health; (6) The remedying of insanitary conditions; (c) The prevention of epidemic diseases. A well-educated sanitary engineer should have a thorough knowledge of general civil engineering, of archi- tecture, and of sanitary science. The practice of the sani- tary engineer embraces water supply, sewerage, and sewage and garbage disposal for cities and for single build- ings; the prevention of river pollution, the improvement of polluted water supplies; street paving and street clean- ing, municipal sanitation, city improvement plans, the laying-out of cities, the preparation of sanitary surveys, the regulation of noxious trades, disinfection, cremation, and the sanitation of buildings. The need of the work of the sanitary engineer in the provision of sewers and drains is thrust upon us in our daily experience by the clogging of sewers, the flooding of streets by heavy rains, filthy conditions in unsewered districts, increased values of prop- erty and improved conditions of living in sewered districts, and in many other ways. The increasing demand for sewerage and the amount of money expended on sewer construction is indicated by the information given in Table I. 2. Historical. An ordinance passed by the Roman Senate in the name of the Emperor about A.D. 80, states: I desire that nobody shall conduct away any excess water without having received my permission or that of my representatives; for it is necessary that a part of the supply flowing from the delivery tanks shall be utilized not only for cleaning our city, but also for flushing the sewers. 1 Neither the sewers mentioned nor the distributing pipes of the public water supply were connected to individual residences. The contributions to the sewers came from the ground and the street surface. The streets were the receptacles of liquid and 1 Frontinus and the Water Supply of Rome, p. 81, by Clemens Herschel. HISTORICAL 3 solid wastes and were often little more than open sewers. A promenade after dark in an ancient, medieval, or early modern city was accompanied not only by the underfoot dangers of an uneven pavement or an encounter with a footpad, but with the overhead danger from the emptying of slops into the streets from the upper windows. Sewers were used for the collection of sur- face water; the discharge of fecal matter into them was pro- hibited. The problem of the collection of sewage remained unsolved until the Nineteenth Century. TABLE 1 POPULATION TRIBUTARY TO SEWERAGE SYSTEMS 1905* 1915f 1920 1 Population discharging raw sewage into the sea or tidal estuaries Population discharging raw sewage into inland streams or lakes Population connected to systems where sewage is treated in some way 6,500,000 20,400,000 1,100,000 8,500,000 26,400,000 6,900,000 Population connected with sewerage sys- tems 28,000,000 41,800,000 46,300 000 * Estimated by G. W. Fuller, Trans. Am. Society of Civil Engineers, Vol. 44, 1905, p. 148. The total population connected with sewerage systems was assumed to be the total population in the United States in cities over 4000 in population. t Estimated by Metcalf and Eddy, American Sewerage Practice, Vol. Ill, p. 240. t Computed from report of the United States Census, 1920, on the same basis as Fuller's estimate for 1905. The development of the London sewers was commenced early in the Nineteenth Century. The sewerage system of Ham- burg, Germany, was laid out in 1842 by Lindley, an English engineer who with other English engineers performed similar work in other German cities because of their earlier experience in English communities. Berlin's present system dates from 1860. The construction of storm water drains in Paris dates from 1663. 1 They were intended only as street drains but are now included in the comprehensive system of the city. The first comprehensive sewerage system in the United States was designed by E. S. Chesbrough for the City of Chicago in 1855. Previous to this 1 Cosgrove, History of Sanitation. 4 INTRODUCTION time sewers had been installed in an indifferent manner and with- out definite plan. The installation of a comprehensive sewerage system in Baltimore in 1915 marks the completion of installation of sewerage systems in all large American cities. In the early days of sewerage design it was considered unsafe to discharge domestic wastes into the sewers as the concentration of so much sewage was expected to create great nuisances and dangers to health. That the fear that the concentration of large quantities of sewage would create a nuisance was not ill founded is proven by the conditions on the Thames at London in 1858-59. Dr. Budd states: l For the first time in the history of man, the sewage of nearly three millions of people had been brought to seethe and ferment under a burning sun in one vast open cloaca lying in their midst. The result we all know. Stench so foul we may w r ell believe had never before ascended to pollute this lower air. Never before at least had a stink risen to the height of an historic event. . . For months together the topic almost monopolized the public prints . . . 'India is in revolt and the Thames stinks' were the two great facts coupled together by a distinguished foreign writer, to mark the climax of a national humiliation. 2 The problem of sewage disposal followed the more or less successful solutions of the problem of sewage collection. In England the British Royal Commission on Sewage Disposal was appointed in 1857 and issued its first report in 1865. The first studies in the United States were started in 1887 by the establish- ment of an experiment station at Lawrence, Massachusetts, where valuable work has been done. The station is under the State Board of Health, which issued its first report containing the results of the work at the station, in 1890. Various methods of sewage treatment preparatory to disposal have been devised from time to time. Some have fallen into disuse, such as the A. B. C. (alum, blood and clay) process, and others have taken a permanent place, such as the septic tank. The unsolved problems of sewage collection, and the number of 1 Sedgwick: Sanitary Science and Public Health. 2 No detrimental effect on the public health was noted as a result of this condition however. It has never been conclusively proven that such nuisances are detrimental to the public health. METHODS OF COLLECTION 5 persons still unserved by sewerage and sewage disposal opens a wide field to the study and construction of sewerage works. 3. Methods of Collection. The method of collection which involves the removal of night soil from a privy vault, the pail system which involves the collection of buckets of human excreta from closets and homes, indoor chemical closets, and other make- shift methods of collection are of extreme importance where no sewers exist, but they are not properly considered as sewerage systems or sewerage works. These methods of collection are generally confined to rural districts and to outlying parts of urban communities. They require constant attention for their proper conduct and little skill for their installation, the principal requirements being to make the receptacles fly-proof. The pneumatic system was introduced by Liernur, a Dutch engineer. 1 It is used in parts of a few cities in Europe, but it is not capable of use on a large scale. It consists of a system of air-tight pipes, connecting water closets, kitchen sinks, etc., with a central pumping station at which an air-tight tank is provided from which the air is partly exhausted. As little water as possible is allowed to mix with the fecal matter and other wastes in order not to overtax the system. Solid and liquid wastes are drawn to the central station when the waste valve on the plumbing fixture is opened. The collection of sewage in a system of pipes through which it is conducted by the buoyant effect and scouring velocity of water is known as the water carriage system. This is the only method of sewage collection in general use in urban communities. In this system solid and liquid wastes are so highly diluted with water as either to float or to be suspended therein. The mixture resulting from this high dilution follows the laws of hydraulics as applied to pure water, or water containing suspended matter. It will flow freely through properly designed conduits and will concentrate the sewage wastes at the point of ultimate disposal. 4. Methods of Disposal. Sewage is disposed of by dilution in water, by treatment on land, or occasionally by discharging it into channels that contain no diluting water. Some form of treat- ment to prepare sewage for ultimate disposal is frequently neces- sary and will undoubtedly be required in a comparatively short time for all sewage discharged into watercourses. The solid 1 Moore and Silcock, Sanitary Engineering, p. 67, 1909. 6 INTRODUCTION matters removed by treatment may be buried, burned, dumped into water, or used as a fertilizer. If the volume of diluting water, or the area and character of land used for disposal are not as they should be, a nuisance will be created. The aim of all methods of sewage treatment has so far been to produce an effluent which could be disposed of without nuisance and in certain exceptional cases to protect public water supplies from pollution. Financial returns have been sought only as a secondary consideration. A few sewage farms and irri- gation projects might be considered as exceptions to this as the value of the water in the sewage as an irrigant has been the primary incentive to the promotion of the farm. It is to be remembered that since the aim of all sewage treat- ment is to produce an effluent that can be disposed of without causing a nuisance, the simplest process by which this result can be attained under the conditions presented is the process to be adopted. No attempt is made to purify sewage completely, or on a practical scale to make drinking water. 5. Methods of Treatment. Screening and sedimentation are the primary methods for the treatment of sewage. By these methods a portion of the floating and settleable solids are removed, preventing the formation of unsightly scum and putrefying sludge banks. Chemicals are sometimes added to the sewage to form a heavy flocculent precipitate which hastens sedimentation of the solid matters in the sewage. The process in these methods is mechanical and the solid matters removed from the sewage must be disposed of by other methods than dilution with the sewage effluent. More complete methods of treatment are dependent on biologic action. Under these methods of treatment complete stabilization of the effluent is approached, and in the most com- plete treatment an effluent is produced which is clear, sparkling, non-odorous, non-putrescible, and sterile. Sterilization of sewage, usually with chlorine or some of its compounds, has been used, not to reduce the amount of diluting water necessary, but to reduce the number of pathogenic germs and to minimize the danger of the transmission of disease. 6. Definitions. Sewage and sewerage are not synonymous terms although frequently confused. Sewage is the spent water supply of a community containing the waste from domestic, industrial or commercial use, and such surface and ground water DEFINITIONS 7 as may enter the sewer. 1 Sewerage is the name of the system of conduits and appurtenances designed to carry off the sewage. It is also used to indicate anything pertaining to sewers. A difference is made between sanitary sewage, storm sew- age, and industrial wastes. Sanitary sewage, sometimes called domestic sewage, is the liquid wastes discharged from residences or institutions, and contains water closet, laundry and kitchen wastes. Storm sewage is the surface run-off which reaches the sewers during and immediately after a storm. Industrial wastes are the liquid waste products discharged from industrial plants. A sewer is a conduit used for conveying sewage. The names of the conduits through which sewage may flow are: Soil Stack. A vertical pipe in a building through which waste water containing fecal matter or urine is allowed to flow. Waste Pipe. A vertical pipe in a building through which waste water containing no fecal matter is allowed to flow. House Drain. The approximately horizontal portion of a house drainage system which conveys the drainage from the soil stack or waste pipe to the point of discharge from the build- ing. House Sewer. The pipe which leads from the outside wall of the building to the sewer in the street. Lateral Sewer. The smallest branch in a sewerage system, exclusive of the house sewers. Sub-main or Branch Sewer. A sewer from which the sewage from two or more laterals is discharged. 2 Main or Trunk Sewer. A sewer into which the sewage from two or more sub-main or branch sewers is discharged. 3 Intercepting Sewer. A sewer generally laid transversely to a sewerage system to intercept some portion or all of the sewage collected by the system. Relief Sewer. A sewer intended to carry a portion of the flow from a district already provided with sewers of insufficient capacity and thus preventing overtaxing the latter. 4 1 Similar to the definition proposed by the Am. Public Health 2 Definition recommended by Am. Public Health Assn. 3 Ibid. 4 Ibid. 8 INTRODUCTION Outfall Sewer. That portion of a main or trunk sewer below all branches. Flushing Sewer. A conduit through which water is conveyed for flushing portions of a sewerage system. Force Main. A conduit through which sewage is pumped under pressure. CHAPTER II WORK PRELIMINARY TO DESIGN 7. Division of Work. Engineering work on sewerage can be divided into four parts, namely: preliminary, design, construc- tion and maintenance. An engineer may be engaged during any one or all of these periods on the same sewerage system, and should therefore be acquainted with his duties during each period. 8. Preliminary. The demand for sewerage normally follows the installation or extension of the public water supply. It may be caused by: a lack of drainage on some otherwise desirable tract of real estate; from a public realization of unpleasant or unhealthful conditions in a built-up district; or through the realization by the municipal administration of the necessity for caring for the future. In whatever way the demand may be created the engineer should take an active part in the promotion of the work. The engineer's duties during the preliminary period are: to make a study of the possible methods by which the demand for sewerage can be satisfied ; to present the results of this study in the form of a report to the committee or organization responsible for the promotion of the work; and so to familiarize himself with the conditions affecting the installation of the proposed plans as to be able to answer all inquiries concerning them. This work will require the general qualities of character, judgment, efficiency and the understanding of men in addressing interested persons individually and collectively on the features of the proposed plans, and the exercise of engineering technique in the survey and the drawing of the plans. The engineer should assure him- self that all legal requirements in the drawing of petitions, adver- tising, permits, etc., have been complied with. This requires some knowledge of national, state, and local laws. Although none the less essential their description is not within the scope of this book. 9 10 WORK PRELIMINARY TO DESIGN The engineer's preliminary report should contain a section devoted to the feasibility of one or more plans which may be explained in more or less detail with a statement of the cost and advantages of each. A conclusion should be reached as to the most desirable plan and a recommendation made that this plan be insta led. Other sections of the report may be devoted to a history of the growing demand, a description of the conditions necessitat- ing sewerage, possible methods of financing, and such other sub- jects as may be pertinent. The making of the preliminary plan and the design of sewerage works are described in subsequent chapters. 9. Estimate of Cost. In making an estimate of cost the information should be presented in a readable and easily compre- hended manner. It is necessary that the items be clearly defined and that all items be included. The method of determining the costs of doubtful items such as depreciation, interest charges, labor, etc., and the probability of the fluctuation of the costs of certain items should be explained. The engineer's estimate may be divided somewhat as follows: Labor. Material. Overhead. This may include construction plant, office expense, supervision, bond, interest on borrowed capital, insurance, transportation, etc. The amount of the item is seldom less than 15 per cent and is usually over 20 per cent of the contract price. Contingencies. This allowance is usually 10 to 15 per cent of the contract price. Profit. This should be from 5 to 10 per cent of the sum of the four preceding items. The contract price is the sum of these items. To this may be added: Engineering. 2 to 5 per cent of the contract price. Extra Work. Zero to 15 per cent of the contract price ; dependent on the character of the work, the completeness of the preliminary information, the completeness of the plans, etc. Legal expense. Purchase of land, rights of way, etc., etc. The cost of the sewer may be stated as so much per linear foot for different sizes of pipe, including all appurtenances ESTIMATE OF COST 11 such as manholes, catch-basins, etc., or the items may be sep- arated in great detail somewhat as follows : Earth excavation, per cu. yd. Rock excavation, per cu. yd. Backfill, per cu. yd. Brick manholes, 3 feet by 4 feet, per foot of depth. Vitrified sewer pipe with cement joints, in place, inches in diameter, to 6 feet deep 6 to 8 feet deep 8 to 10 feet deep Repaving, macadam per sq. yd. asphalt per sq. yd. Flush tanks, gal. capacity, per tank. Service pipes to flush tanks, per linear foot., etc., etc. These methods represent the two extremes of presenting cost estimates. Each method, or modification thereof, may have its use, dependent on circumstances. Reliable cost data are difficult to obtain. Lists of prices of materials and labor are published in certain engineering and trade periodicals. The Handbook of Cost Data by H. P. Gillette contains lists of the amount of material and labor used on certain specific jobs and types of construction. The price of labor and materials on the local market can be obtained from the local Chamber of Commerce, contractors and other employers of labor, and dealers in the desired commodities. Contract prices for sewerage work published in the construction news sections of engineering periodicals may be a guide to the judgment of the probable cost of proposed work, but are generally dangerous to rely upon as full details are lacking in the description of the work. A wide experience in the collection and use of cost data is the desirable qualification for making estimates of cost. It is pos- sessed by few and is not an infallible aid to the judgment. Having completed the design and summary of the bills of material and labor necessary for each structure or portion of the sewerage system, the product of the unit cost and the amount of each item plus an allowance for overhead will equal the cost of the item. The total cost will be the sum of the costs of each item. The items should be so grouped that the cost of the differ- ent portions of the system are separated in order that the effect on the total cost resulting from different combinations of items or the omission of any one item may be readily computed. 12 WORK PRELIMINARY TO DESIGN A method for estimating the approximate cost of sewers, devised by W. G. Kirchoffer 1 depends upon the use of the diagram shown in Fig. 2. The factors for local conditions are shown in Table 2. For example, let it be required to find the cost of a 15-inch vitrified pipe sewer at a depth of 9 feet, if the unit costs Diameter of Vitrified Pipe in Inches. 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 30 20 30 40 50 60 70 80 90 j^ 2 3456 'Cost of Sey/er in Dollars per Lineal Foot. 7 8 9 10 II 12 14 16 IS FIG. 2. Diagram for Estimating the Cost of Sewers. Eng. News, Vol. 76, p. 781. of labor and material and the conditions are the same as shown in Table 3. Solution First: To find the factor depending on local condi- tions, enter the diagram at the 10-inch diameter and continue down until the intersection with the depth of trench at 8.2 feet is found. Now go diagonally parallel to lines running from left to right upwards to the inter- 1 Eng. News, Vol. 76, 1916, p. 781. See also Eng. News-Record, Vol. 85, 1920, pp. 22, 1175. ESTIMATE OF COST 13 section with the vertical line through a cost of 45 cents per foot. The diagonal line running from left to right downwards through this intersection corresponds to a factor of about 11. TABLE <*, FACTORS FOR COSTS OF SEWERS TO BE USED WITH FIGURE 2 Character of Material Factor Character of Material Factor Clay, gravel and boulders, Medford Mostly sand, deep trenches 22-26 Clay 2 miles inland. Laborers boarded at sanitarium, Wales 35 sheeted. Wages medium. Richland Center 21-22 Clay, gravel and boulders at Plymouth 20-27 Sandy clay. Wages medium. Labor conditions good at Kiel 15-20 Sand, clay and good digging at Lake Mills Red clay Machine work at 16-19 Sand. Sandy clay, some North Milwaukee 20-24 water. Labor conditions good. Pipe prices medium at Manston 14-20 Good digging. Wages me- dium at West Salem Sandy soil bracing only re- 17-19 Gravelly clay, i^th laid in concrete at Burlington 13-22 quired. No water. Wages and pipe medium 14 Sandy clay, some water, sheet- Red sticky clay 24 ing at La Farge Sand with water 17-23 20 Good digging in any soil Work scarce. 15 Gravel and boulders. High wages 26 Red clay. No bracing Work inland from railroad 20 Clay soil. Good digging. . . . Sandy clay. Some water. . . . 17 23 Boarding laborers and other expenses 35 Second: To find the cost of 15-inch pipe at a depth of 9.0 feet, enter the diagram at a diameter of 15 inches and continue down until the intersection with a depth of trench at 9 feet is found. Now go diagonally parallel to lines running from left to right upwards to the intersection with the diagonal line running from left to right downwards corresponding to the factor of 11 found above. The vertical line passing through this point shows the cost to be 67 cents per foot. 14 WORK PRELIMINARY TO DESIGN TABLE 3 COST OF SEWER CONSTRUCTION AT ATLANTIC, IOWA (From Gillette's Handbook of Cost Data) Material : Clay, not difficult to spade and requiring little or no bracing and practically no pumping. All hand work except backfill which was done by team and scraper. Depth of trench averaged 8.2 feet; width 30 inches. Diameter of pipe 10 inches. Wage, Cost, Wage, Cost, Item Cents Cents Item Cents Cents per per per per Hour Foot. Hour Foot. Pipe 0.20 Trenching. Bracing Hauling team and men 17 002 driver 30 003 Backfilling Shovel 17 010 Hauling. Man help- Backfilling. Team ing 17 001 and scraper 30 008 Cement and sand . . . .006 Backfilling. Man Pipe layers 22 .014 and scraper. . . . 17 005 Pipe layer's helper. . 17 .014 Water boy 10 .006 Trenching. Top men 17 .027 Foreman 30 022 men 17 130 Total 450 Trenching. Scaffold 17 .002 men . . 17 002 METHODS OF FINANCING The construction of sewerage works may be paid for by the issue of municipal bonds, by special assessment, by funds available from the general taxes, or by private enterprise. 10. Bond Issues. A municipal bond is a promise by the municipality to pay the face value of the bond to the holder at a certain specified time, with interest at a stipulated rate during the interim. The security on the bond is the taxable property in the municipality. The legal restrictions thrown around muni- cipal bond issues, the value of the taxable property in the munici- pality, all of which may be used as security for municipal bonds, and the fact that a municipality can be sued in case of default, make municipal bonds desirable and provide a good market for SPECIAL ASSESSMENT 15 their sale. The funds available from a municipal bond issue are limited by the amount that the legal limit is in excess of the out- standing issues. The legal limit varies in different states from about 5 to 15 per cent of the assessed value of the property in the municipality. In some cases the amount available from municipal bonds has been increased by forming a municipality within a municipality such as a sanitary district, a park district, a drainage district, etc., which comprises a large portion or all of an existing municipal corporation. This case is well illustrated in some parts of the City of Chicago where the municipal taxing powers are shared by the City government, the Sanitary District, and Park Commissioners. The right to create a new municipal corporation must be granted by the state legislature. Knowledge of fixed bonds, serial bonds, life of bonds, sinking funds, etc. is an important part of an engineer's education. 1 Bond issues must usually be presented to the voters for approval at an election. If approved, and other legal procedure has been followed, the bonds may be bought by some of the many bonding houses, or by private individuals, and the money is immediately available for construction. The bonds are redeemed by general taxation spread over the period of the issue. 11. Special Assessment. A special assessment is levied against property benefited directly by the structure being paid for. Special assessments are used for the payment for the construction of lateral sewers which are a direct benefit to separate districts but are without general benefit to the city. In case the construc- tion of an outfall sewer or the erection of a treatment plant, which may be of some general benefit, is necessary to care for a separate district, a part of the expense may be borne by funds available from general taxation. The legal procedure for the raising of funds by special assessment and the purpose to which the funds so raised may be applied are stipulated in great detail in different states and their directions must be followed implicitly. Illinois procedure, which is similar to that in some other states, is as follows : a meeting of the interested property owners is called by a committee or board of the municipal government, as the result of a petition by interested persons or through the inde- pendent action of the Board. At this preliminary meeting or 1 For a more extensive treatment of the subject see Principles and Methods of Municipal Administration by W. B. Munro, 1916. 16 WORK PRELIMINARY TO DESIGN public hearing arguments for and against the proposed improve- ment are heard. The engineer is present at this meeting to answer questions and to advise concerning the engineering features of the plan. If approval is given by the Board the plan and specifications are prepared complete in every detail and incorporated in an ordinance which is presented to the legislative branch of the city government for passage. If the project is adopted it is taken to the county court. An assessment roll is prepared by a commissioner appointed by the court. This roll shows the amount to be assessed against each piece of property benefited. A hearing is then held in the county court at which the owner of any assessed property may voice objections to the .continuation of the project. The project may be thrown out of cougrt for many different reasons, such as the misspelling of a street name, an error in an elevation, an error in the description of a pavement, but most important of all is definite proof that the benefit is not equal to the assessment. The many minor irregu- larities which may nullify the procedure in a special assessment differ in different states and in different courts in the same state, but in general no court can approve an assessment greater than the benefits given. After the project has passed through the county court and the assessment roll has been approved, bonds may be issued for the payment of the contractor. Special assess- ment bonds are liens against the property assessed and have not the same security as a general municipal bond. For this reason a city which has reached its legal limit of municipal bond issues can still pay for work by special assessment. The funds available from special assessments are limited only by the benefit to the property assessed. The amount of the benefit is difficult to fix and may lead to much controversy. It should not exceed the amount demanded for similar work in other localities, unless unusual and well-understood reasons can be given. 12. General Taxation. In paying for public improvements by general taxation the money is taken from the general municipal funds which have been apportioned for that purpose by the legislative department of the municipal government. This method of raising funds for sewerage construction is seldom used unless the political situation is unfavorable to the success of a bond issue or special assessment and the need for the improvement PREPARING FOR DESIGN 17 is great. It is usually difficult to appropriate sufficient funds for new construction as the general tax is apportioned to support only the operating expenses of the city, and statutory provisions limit the amount of tax which can be levied. 13. Private Capital. Private capital has been used for financ- ing sewerage works in some cases because of the aversion of the public in some cities to the payment of a tax for the negative service performed by a sewer. Sewers are buried, unseen, and frequently forgotten, but knowledge of their necessity has spread and the number of privately owned sewerage works is diminishing because of the better service which can be provided by the munici- pality. Franchises are granted to private companies for the construc- tion of sewers only after the city has exhausted other methods for the raising of capital. The return on the private capital invested is received from a rental paid by the city, or paid directly by the users of the system, an initial payment usually being demanded for connection to the system. To be successful the enterprise must be popular and must fill a great need. This method of financing sewerage works is seldom employed as favorable con- ditions are not common. PRELIMINARY WORK 14. Preparing for Design. Methods for the design of sewerage systems are given in Chapter V. Before the design is made certain information is essential. A survey must be made from which the preliminary map can be prepared as described in Art. 42. Other necessary information which is the basis of subsequent estimates of the quantity of sewage to be cared for must be obtained by a study of rates of water consumption and the density and growth of population, the measurement of the discharge from existing sewers, and the compilation of rainfall and run-off data. If no rainfall data are available estimates must be made from the nearest available data. Observations of rainfall or run-off for periods of less than 10 to 20 years are likely to be misleading. Methods for gathering and using this information are explained in subsequent chapters. Underground surveys are desirable along the lines of the proposed sewers to learn of obstructions, difficult excavation 18 WORK PRELIMINARY TO DESIGN and other conditions which may be met. All such data are seldom gathered except for sewerage systems involving the expenditure of a large amount of money. For construction in small towns or small extensions to an existing system the funds are usually insufficient for extensive preliminary investigation. The saving in this respect is paid unknowingly to the contractor as com- pensation for the risk in bidding without complete information. 15. Underground Surveys. These may be more or less exten- sive dependent on the character of the district in which construc- tion is to take place. In built-up districts the survey should be more thorough than in sparsely settled districts where only the character of the excavated material is of interest and no obstruc- tions are to be met. Underground surveys furnish to the engineer and to prospect- ive bidders on contract work information on which the design and estimate of cost and the contractor's bid may be based and without which no intelligent work can be done. By removing much of the uncertainty of the conditions to be met in the con- struction of the sewer, the design can be made more economical and the contractor's btd should be markedly lower, sufficiently so to repay more than the expense of the survey. The information to be obtained consists of the location of the ground-water level, and the location and sizes of water, gas, and sewer pipes, tele- phone and electric conduits, street-car tracks, steam pipes, and all other structures which may in any way interfere with subsurface construction. These structures should be located by reference to some permanent point on the surface. The elevation of the top of the pipes, except sewers, rather than the depth of cover should be recorded, as the depth of cover is subject to change. The elevation of sewers should be given to the invert rather than to the top of the pipe. A portion of the map of the subsurface conditions at Wash- ington, D. C., is shown in Fig. 3. Many of the dimensions and notations are not shown to avoid confusion on this small repro- duction. 1 Colors are generally used instead of different forms of cross hatching to show the different classes of pipe and structures. In addition to a record of the underground structures the char- acter of the ground and the pavement should be recorded. A comprehensive underground survey is seldom available nor does 1 Eng. Record, Vol. 74, 1916, p. 263. UNDERGROUND SURVEYS 19 ill ! S 5 11, & co Q. 3 co <*, sJ r*u S s 8 1 H a ij Is" If! ;!* llt 20 WORK PRELIMINARY TO DESIGN time usually permit its being made preliminary to the design of a sewerage system. The character of the material through which the sewer is to pass should be determined in all cases. Underground pipes and structures are located by excavations, which may be quite extensive in some cases. Their position is fixed by measurements referred to manholes and other under- ground structures which are somewhat permanent in position. A city engineer should grasp every opportunity to record underground structures when excavations are made in the streets. The character of the material through which the sewer is to pass is determined by borings. 16. Borings. Methods used for the investigation of subsurface conditions preliminary to sewer con- struction are: punch drilling, boring with earth auger, jet boring, wash boring, percussion drilling, abrasive drilling, and hydraulic drilling. The last three methods named are used only for unusually deep borings or in rock. Punch drills are of two sorts. The simplest punch drill consists of an iron rod f of an inch to 1 inch in diameter, in sections about 4 feet long. One section is sharpened at one end and threaded at the other so that the next section can be screwed into it with- ou t increasing the diameter of the rod, as shown in Fig. 4. The drill is driven by a sledge striking upon a piece of wood held at the top of the drill to pre- vent injury to the threads. The drill should be turned as it is driven to prevent sticking. It is pulled out by a hook and lever as shown in Fig. 5. It is useful in soft ground for soundings up to 8 to 12 feet in depth. Another form of punch drill described by A. C. Veatch 1 consists of a cylinder of steel or iron, one to two feet long split along one side and slightly spread. The lower portion is very slightly expanded and tempered into a cutting edge. In use it is attached to a rope or wooden poles and lifted and dropped in the hole by means of a rope given a few turns about a windlass or drum. By this process the material is forced up into the bit, slightly springs it, and so is held. When the bit is filled it is raised to the surface and emptied. Much 1 Professional paper No. 46, United States Geological Survey, 1906, p. 97. FIG. 4. Punch Drill. BORINGS 21 FIG. 5, Lever for Pulling Punch Drill. deeper holes can be made with this than with the sharpened solid rod. Types of earth augers about 1J- inches in diameter are shown in Fig. 6. They are screwed on to the end of a section of the pipe or rod and as the hole is deepened successive lengths of pipe or rod are added. The device is operated by two men. It is pulled by straight lifting or with the assistance of a link and ^^ '_ j. ^ ^_., CT lever similar to that shown I in Fig. 5. The device is suitable for soft earth or sand free from stones, and can be used for holes T5 to 25 feet in depth. For deeper holes a block and tackle should be used for lifting the auger from the hole. It is not suitable for holes deeper than about 35 feet. In the jetting method water is led into the hole through a f -inch or 1-inch pipe, and forced down- ward through the drill bit or nozzle against the bot- tom of the hole. The complete equipment is shown in Fig. 7. 1 It is not always necessary to case the hole as shown in the figure as the muddy FIG. 6. Earth Augers. water and the vibration 1 United States Geological Survey, Water Supply paper No. 257, 1911. 22 WORK PRELIMINARY TO DESIGN Drive Weight Wooden Platform Clamped to Casing Wooden Buffer Drive Head Force Pump -2- Z)r/Ve Weight Rope to Hoisting Drum orSpool -Drill Rod Pope to Hoisting Drum - Pope Supporting Drill Rods Clamp orWrench // Qg. ,'PubberHosefofa for Turning Drill Pipe " Drive Weight. Pump / Pipe Wrench for < Turning Casing Poo I to Supply Pump FIG. 7. Jetting Outfit. U. S. Geological Survey, Water Supply Paper, No. 257 1. Simple Jetting Outfit. 2. Jetting Process. 3. Common Jetting Drill. 4a and 46. Expansion Bit or Paddy. 5. Drive Shoe. BORINGS 23 of the pipe puddle the sides so that they will stand alone. The jet pipe may be churned in the hole by a rope passing over a block and a revolving drum. In suitable soft materials such as clay, sand, or gravel, holes can be bored to a depth of 100 feet and samples collected of the material removed. An objection to the method is the difficulty of obtaining sufficient water. Methods of drilling in rock up to depths of 20 feet are described in Chapter XI under Rock Drilling. For deeper holes percussion, abrasive, or hydraulic methods as used for deep well drilling must be employed. CHAPTER III QUANTITY OF SEWAGE 17. Dry-weather Flow. Estimates of the quantity of dry- weather sewage flow to be expected are ordinarily based on the population, the character of the district, the rate of water con- sumption, and the probable ground-water flow. Future condi- tions are estimated and provided for, as the sewers should have sufficient capacity to care for the sewage delivered to them during their period of usefulness. 18. Methods for Predicting Population. Methods for the prediction of future population are given in the following para- graphs. The method of graphical extension. This is the quickest and most simple of all. In this method a curve is plotted on rect- angular coordinates to any convenient scale, with population as ordinates and years as abscissas. The curve is extended into the future by judgment of its general tendency. An example is given of the determination of the population of Urbana, Illinois, in 1950. Table 4 contains the population statistics which have been plotted on line A in Fig. 8 and extended to 1950. The probable population in 1Q50 is shown by this line to be about 21,000. The method of geometrical progression. In this method the rate of increase during the past few years or decades is assumed to be constant and this rate is applied to the present population to forecast the population in the future. For example the rate of increase of population in UrbaTia for the past 7 decades has varied widely, but indications are that for the next few decades it will be about 20 per cent. Applying this rate from 1920 to 1950 the population in 1950 is shown to be about 17,800. It is evident that this method may lead to serious error as insufficient information is given in the table to make possible the selection of the proper rate of increase. 24 METHODS FOR PREDICTING POPULATION 25 TABLE 4 POPULATION STUDIES Urbana, Illinois Population of Abso- Per Year Ann Popu- lation lute Increase for Each Cent Increase forEach Decatur Dan- ville Cham- paign Kanka- kee Peoria Bloom- ington Arbor, Michi- Decade Decade gan 1850 210 736 5,095 1,594 1860 2,038 1828 85.6 3,839 1,632 1,727 2,984 14,045 7,075 5,097 1870 2,277 239 10.5 7,161 4,751 4,625 5,189 22,849 14,590 7,368 1880 2,942 665 22.6 9,547 7,733 5,103 5,651 29,259 17,180 8,061 1890 3,511 569. 16.2 16,841 11,491 5,839 9,025 41,024 20,484 9,431 1900 5,728 2217 38.7 20,754 16,354 9,098 13,595 56,100 23,286 14,509 1910 8,245 2517 30.5 31,140 27,871 12,421 13,986 66,950 25,786 14,817 1920 10,230 1985 19.4 43,818 33,750 15,873 16,721 76,121 28,638 19,516 Decades in Life of City of Urbana 1870 1880 1890 1900 1910 1920 1930 1940 1950 50,000 40,000 / / L anvill ; mingh ..'--' ,1*1 A 1 u '/ Bloo rbana jn^, OguT rfjjfe *2 tfOt ^x* {R f .. f /I ( / '//^ -Ann Arbor Chan paigj U*j iA* ^ & -Kan Location X a K* Building * 03 M > Hotel Biltmore. . . . 470 368 78th-79th St. and McGraw Bldg 309 206 Hotel McAlpin. . . . 753 694 B'way 256 192 N. Y. Telephone Hotel Pla/a. ...... 630 578 410 E. 65th St 350 295 Bldg 194 Hotel Waldorf 30th St. and Madi- Met. Life Bldg.. . 256 Astoria 618 482 son Ave 306 188 42d St. Bldg 271 Hotel Astor 732 492 27 Lewis St 307 250 Municipal Bldg. . . 118 Hotel Vanderbilt . . 604 545 258 Delancey St . . 267 226 Equitable Bldg 366 268 Average 634 526 Average 297 230 Average 338 219 * Max. represents only the average maximum, not the greatest maximum. TABLE 10 SEWAGE FLOW FROM DIFFERENT CLASSES OF DISTRICTS BASED ON 1915 REPORT OF MILWAUKEE SEWERAGE COMMISSION Ratio of maximum to average rate for department store district Ratio of maximum to average rate for hotel district Ratio of maximum to average rate for office building district Ratio of maximum to average rate for wholesale commercial district. 1.755 1.65 1.51 2.1 Average and maximum gallons per thousand square feet of Avg. Max. n noor area . For department store district 232 407 For office building district 541 891 For wholesale commercial district 164 344 For all districts except wholesale commercial 381 618 Average and maximum gallons per day : For all districts except wholesale commercial 17,700 29,800 For wholesale commercial district 9,650 20,000 36 QUANTITY OF SEWAGE TABLE 11 RATES OF CONSUMPTION PREDICTED FOR DIFFERENT DISTRICTS IN NEW YORK CITY .8 is 4* o O o< I I J M<^ SJ t d+J .Sg O .si 1 P"; sj aj District eS t, (S 3.1 1 3d- 60 en . C o* oS 1 II l! || ?| || III a g| T3 III 3! l ll ll "o "w ^ 4) W*J bi > j& 11 '3s o -o o o oo O O5 O i i ^F OS 00 t^. Oi i-irji oir^ : :PQ -8 - - PL, .pi, . . .pH . :>: : 40 QUANTITY OF SEWAGE tion and assume the sewage flow to equal the water consumption; determine the maximum and minimum rates of sewage flow; and finally, estimate the maximum rate of ground water seepage and add it to the maximum rate of sewage flow to give the total quantity of sewage to be carried by the proposed sewers. QUANTITY OF STORM WATER 28. The Rational Method. The water which falls during a storm must be removed rapidly in order to prevent the flooding of streets and basements, and other damages. The quantity of water to be cared for is dependent upon: the rate of rainfall, the character and slope of the surface, and the area to be drained. All methods for the determination of storm water run-off, whether rational or empirical, depend upon these factors. The so-called Rational Method can be expressed algebraically, as, Q = AIR, in which Q = rate of run-off in cubic feet per second; A = area to be drained expressed in acres; 7 = percentage imperviousness of the area; R maximum average rate of rainfall over the entire drainage area, expressed in inches per hour, which may occur during the time of concentration. The area to be drained is determined by a survey. A discussion of R and 7 follows in the next two sections. An example of the use of the Rational Method is given on page 95. 29. Rate of Rainfall. Rainfall observations have been made over a long period of time by United States Weather Bureau observers and others. Continuous records are available in a few places in this country showing rainfall observations covering more than a century. Such records have been the bases for a number of empirical formulas for expressing the probable maximum rate of rainfall in inches per hour, having given the duration of the storm. Table 13 is a collection of these formulas with a statement as to the conditions under which each formula is appli- cable. The formula most suitable to the problem in hand should be selected for its solution. 1 1 A comprehensive discussion of rainfall formulas will be found in Vol. 54 of the Transactions Am. Society of Civil Engineers, 1905. RATE OF RAINFALL 41 TABLE 13 RAINFALL FORMULAS Name of Originator Conditions for which Formula is Suitable Formula E S Dorr 150 A. N. Talbot. . .. A. N.Talbot Emil Kuichling. . . L. J. LeConte.... Sherman Sherman Webster Hendrick Maximum storms in Eastern United States Ordinary storms in Eastern United States J+30 . 360 105 2- 120 i= , etc. Z+20' 105 Heavy rainfall near New York City. . For San Francisco. See T. A. S. C. E. v 54 p 198 Maximum for Boston, Mass Extraordinary for Boston, Mass Ordinary for Philadelphia, Pa Ordinary storms for Baltimore. Eng. & Cont., Aug. 9. 1911 J. de Bruyn-Kops. C D. Hill Metcalf and Eddy W.W. Horner.... R.A Brackenbu} Metcalf and Eddy Metcalf and Eddy Kenneth Allen . . . . 163 Ordinary storms for Savannah, Ga . . . . For Chicago 111 t+27 120 % " Louisville, Ky. Am. Sew. Prac., Vol I. St. Louis, Mo. Eng. News, Sept. 29, 1910 For Spokane, Wash. Eng. Record, Aug. 10 1912 84 400 * New Orleans For Denver, Colo Central Park, N. Y 51-Year Record. Eng. News-Record, April 7, 192 1, p 588 2J+40 * Formula devised by H. E. Babbitt from Allen's 25-year curve. 30. Time of Concentration. By the time of concentration is meant the longest time without unreasonable delay that will be required for a drop of water 1 to flow from the upper limit of a drainage area to the outlet. Assuming a rainfall to start sud- 1 See Note under Table 14. 42 QUANTITY OF SEWAGE denly and to continue at a constant rate and to be evenly dis- tributed over a drainage area of 100 per cent imperviousness and even slope towards one point, the rate of run-off would increase constantly until the drop of water from the upper limit of the area reached the outlet, after which the rate of run-off would remain constant. In nature the rate of rainfall is not constant. The shorter the duration of a storm the greater the intensity of rain- fall. Therefore the maximum run-off during a storm will occur at the moment when the upper limit of the area has commenced to contribute. From that time on the rate of run-off will decrease. The time of concentration can be measured fairly well by observing the moment of the commencement of a rainfall, and the time of maximum run-off from an area on which the rain is falling. A prediction of the time of concentration is more or less guess work. As the result of measurements some engineers assume the time of concentration on a city block built up with impervious roofs and walks, and on a moderate slope, is about 5 to 10 minutes. This is used as a basis for the judgment of the time of concentra- tion on other areas. For relatively large drainage areas such a method cannot be used. The procedure is to measure the length of flow through the drainage channels of the area,, to assume the velocity of the flood crest through these channels and thus to determine the time of concentration. Table 14 shows the flood crest velocities in various streams of the Ohio River Basin under flood conditions. The velocity over the surface of the ground may be approximated by the use of the formula 1 V = 2,0007 VS, in which V = the velocity of flow over the surface of the ground in feet per minute; J = the percentage imperviousness of the ground; $ = the slope of the ground. For areas up to 100 acres where natural drainage channels are not existent this formula will give more satisfactory results than guesses based on the time of concentration of certain known areas. Having determined the time of concentration, the rate of rain- fall R to be used in the Rational Method is found by substitution in some one of the rainfall formulas given in Table 13. 1 Sewerage by A. P. Folwell. TIME OF CONCENTRATION 43 s s si PQ a & D CREST VELOCITI From Table 12, U. F - S-S.9 g +- 1 JH f-t 02 ^ iplii ^> cr 2 $ 3 O^^fM^r-l OO5C' 1 *OiO-OOiOOTt<-^ T-iO lO CO -H I-H O5 (M iM CO CO CO C<1 rt< rt< iO (N CO S C^OOrH QO b- l- r^OO O i 8(N(N 00 i i CO QO CO O -^ O ^H 53 03 f< j- s-^i^"ssisij ^O- 3 r-d3'c3^^3 .rO ro^ ity ver he f i' ** 2* i; SI II * o *"^ "o** S2 s: ie in > P JS^d 1U HS |'C 1M 2-g.g Us i sJS 44 QUANTITY OF SEWAGE 31. Character of Surface. The proportion of total rainfall which will reach the sewers depends on the relative porosity, or imperviousness, and the slope of the surface. Absolutely impervi- ous surfaces such as asphalt pavements or roofs of buildings will give nearly 100 per cent run-off regardless of the slope, after the surfaces have become thoroughly wet. For unpaved streets, lawns, and gardens the steeper the slope the greater the per cent of run-off. When the ground is already water soaked or is frozen the per cent of run-off is high, and in the event of a warm rain on snow covered or frozen ground, the run-off may be greater than the rainfall. The run-off during the flood of March, 1913, at Columbus, Ohio, was over 100 per cent of the rainfall. Table 15 l shows the relative imperviousness of various types of surfaces when dry and on low slopes. The estimates for relative impervious- ness used in the design of the Cincinnati intercepter are given in Table 16. TABLE 15 VALUES OF RELATIVE IMPERVIOUSNESS Roof surfaces assumed to be watertight . 70-0 . 95 Asphalt pavements in good order 85- . 90 Stone, brick, and wood-block pavements with tightly cemented joints 75- . 85 The same with open or ancemented joints 50- . 70 Inferior block pavements with open joints 40- . 50 Macadamized roadways 25- . 60 Gravel roadways and walks 15- . 30 Unpaved surfaces, railroad yards, and vacant lots 10- . 30 Parks, gardens, lawns, and meadows, depending on surface slope and character of subsoil 05- . 25 Wooded areas or forest land, depending on surface slope and char- acter of subsoil 01- .20 Most densely populated or built up portion of a city 70- .90 C. E. Gregory 2 states that /, in the expression Q = AIR is a function of the time of concentration or the duration of the storm. If t represents the time of concentration and T represents the duration of the storm, then when T is less than t 7=0.175**, 1 From an article by E. Kuichling in Transactions American Society of Civil Engineers, Vol. 65, 1909, p. 399. 2 Trans. Am. Society Civil Engineers, Vol. 58, 1907, p. 483. CHARACTER OF SURFACE 45 I'll 1 03 sjli "S w d ^"S 15 OS n Q " cc 3 81-oi Is ^ 4> < OOrHTj< CO CO O^ OOOO-* i-H OS O H 02 ill l <*eo-i OM I-HCC IC^HT^O t^t^ 1-H 1C 8 H '^>< "o < hH g ifl 1 O % "2*9 c io_. . oS .i2 St2 {2 : : : 2 : : 3 "g 1 d w fl -*^ 02 H-4 3 I fl-^ H H^O o| :s: s" :s ; ;: j : ; ; o 1 5 ^is (IP M oo w Q 2"m 8 g 6 ^' S si^ OOC^CJ COO N I-H -O T}< odd CIN oo co *od ' ' OOOt- MC^ ^- -CO OS i o w H * d o lt f t ' ' OiC * t- g J C5 1 .isl 'a ao o-fn (U" 00 :; - s g s ; ;; B P . jil . . 00 00 000 ... t/J 0^^ ^_J"oQ ^ . ! ! . . . . ... ! ! ! ! m H S H ~" cj 1 . .... TM g -02 S to s . +> l! wlj iC O t** 1C iC O ^ GO " .' ' d OO OO -HCO'I-I ... tO -< 1-H .... o 8 ffi M*^3 A^ W r ^ ^ PH S S a "a fl 08 -"2+5 C*l ^C O -H CO ^C ^ C^l (N HH fa 'IP l' s ll i-l ;; t>d dd icViwj ; '.'.'. ec H ^05 | z w "S G ^ IN : : : ; : ; fe 3 i i : : .* S si w 5 Q ,^ 3 ^ bO . 5 a 1 i n i ij ill O g HH .2 M ! : : 2^' ^ " o b 1 1 gs-S J : : a-3g1 ^>>l I SJ jgS | j-g ^ j| >^|.^ ||| 1 6 H 1 - |fS( |o |fflo |loSo |H!Z; 11 PH 02 M P M 46 QUANTITY OF SEWAGE but when T is greater than t, Gregory condenses Kuichling's rules with regard to the per cent run-off, as follows: 1. The per cent of rainfall discharged from any given drainage area is nearly constant for heavy rains lasting equal periods of time. 2. This per cent varies directly with the area of imper- vious surface. 3. This per cent increases rapidly and directly or uni- formly with the duration of the maximum intensity of the rainfall until a period is reached which is equal to the time required for the concentration of the drainage waters from the entire area at the point of observation, but if the rain- fall continues at the same intensity for a longer period this per cent will continue to increase at a much smaller rate. 4. This per cent becomes larger when a moderate rain has immediately preceded a heavy shower on a partially permeable territory. Gregory's formulas have not been generally accepted and are not widely used in practice. Marston stated : l All that engineers are at present, warranted in doing is to make some deduction from 100 per cent run-off . . . the deduction . . . being at present left to the engineer in view of his general knowledge and his familiarity with local conditions. Burger states 2 in the same connection : In its application there will usually be as many results (differing widely from each other) as the number of men using it. In spite of these objections the Rational Method is in more favor with engineers than any other method. 32. Empirical Formulas. The difficulty of determining run- off with accuracy has led to the production by engineers of many empirical formulas for their own use. Some of these formulas have attracted wide attention and have been used extensively, 1 Trans. American Society of Civil Engineers, Vol. 58, 1907, p. 498. 2 Ibid. EMPIRICAL FORMULAS 47 in some cases under conditions to which they are not applicable. In general these formulas are expressions for the run-off in terms of the area drained, the relative imperviousness, the slope of the land, and* the rate of rainfall. The Burkli-Ziegler formula, devised by a Swiss engineer for Swiss conditions and introduced into the United States by Rudolph Hering, was one of the earliest of the empirical formulas to attract attention in this country. It has been used extensively in the form Q-CM-Jg, in which Q = the run-off in cubic feet per second; i = the maximum rate of rainfall in inches per hour over the entire area. This is determined only by ex- perience in the particular locality, and is usually taken at from 1 to 3 inches per hour; = the slope of the ground surface in feet per thousand, A = the area in acres; C = an expression for the character of the ground sur- face, or relative imperviousness. In this form of the expression C is recommended as 0.7. The McMath formula was developed for St. Louis conditions and was first published in Transactions of the American Society of Civil Engineers, Vol. 16, 1887, p. 183. Using the same notation as above, the formula is, McMath recommended the use of C equal to 0.75, i as 2.75 inches per hour, and S equal to 15*. The formula has been extended for use with all values of C, i, S, and A ordinarily met in sewerage practice. Fig. 11 is presented as an aid to the rapid solution of the formula. Other formulas have been devised which are more applicable to drainage areas of more than 1,000 acres. 1 Such areas are met in the design of sewers to enclose existing stream channels drain- ing large areas. Kuichling's formulas, published in 1901 in the 1 The principles governing the run-off from large areas are explained in Elements of Hydrology, by A. F. Meyer, 1917. QUANTITY OF SEWAGE r : 20 -30 -40 ^60 ^80 100 200 ^300 -400 500 ^600 iisoo ^1000 3000 -4000 5000 : 6000 ^8000 : .10,000 Values of c 0.1 0.2 0.30.40.5 0.7 1.0 FIG. 11. Diagram for the Solution of McMath's Formula, EMPIRICAL FORMULAS 49 report of the New York State Barge Canal, were devised for areas greater than 100 square miles. The following modification of these formulas for ordinary storms on smaller areas was published for the first time in American Sewerage Practice, Volume I, by Metcalf and Eddy : 25000 + 30 40 50 60 70 Quantity in Cubic Feet per Second. FIG. 12. Comparison of Empirical Run-off Formulas. It is to be noted that the only factor taken into consideration is the area of the watershed. It is obvious that other factors such as the rate of rainfall, slope, imperviousness, etc., will have a marked effect on the run-off. There are other run-off formulas devised for particular con- ditions, some of which are of as general applicability as those quoted. Two formulas which are frequently quoted are: Fan- ning's, Q = 2QQM 5/ * and Talbot's Q = 500M M , in which M is the area of the watershed in square miles. A comprehensive treatment of the subject is given in American Sewerage Practice, Vol. I, by Metcalf and Eddy. A comparison of the results obtained by the application of a few formulas to the same conditions is shown graphically in Fig. 12. It is to be noted that the divergence between the smallest 50 QUANTITY OF SEWAGE and largest results is over 100 per cent. As these formulas are not all applicable to the same conditions, the differences shown are due partially to an extension of some of them beyond the limits for which they were prepared. 33. Extent and Intensity of Storms. In the design of storm sewers it is necessary to decide how heavy a storm must be pro- vided for. The very heaviest storms occur infrequently. To build a sewer capable of (faring for all storms would involve a prohibitive expense over the investment necessary to care for the ordinary heavy storms encountered annually or once in a decade. This extra investment would lie idle for a long period entailing a considerable interest charge for which no return is easily seen. The alternative is to construct only for such heavy storms as are of ordinary occurrence and to allow the sewers to overflow on exceptional occasions. The result will be a more frequent use of the sewerage system to its capacity, a saving in the cost of the system, and an occasional flooding of the district in excessive storms. The amount of damage caused by inundations must be balanced against the extra cost of a sewerage system to avoid the damage. A municipality which does not provide adequate storm drainage is liable, under certain circumstances, for damages occasioned by this neglect. It is not liable if no drainage exists, nor is it liable if the storm is of such unusual character as to be classed legally as an act of God. Kuichling's studies of the probabilities of the occurrence of heavy storms are published in Transactions of the American Society of Civil Engineers, Vol. 54, 1905, p. 192. Information on the extent of rain storms is given by Francis in Vol. 7, 1878, p. 224, of the same publication. Kuichling expresses the intensity of storms which will occur, . in . 105 once in 10 years as i . 1C .120 once in 15 years as i = in which i is the intensity of rainfall in inches per hour and t is the duration of the storm in minutes. CHAPTER IV THE HYDRAULICS OF SEWERS 34. Principles. The hydraulics of sewers deals with the application of the laws of hydraulics to the flow of water through conduits and open channels. In so far as its hydraulic proper- ties are concerned the characteristics of sewage are so similar to those of water that the same physical laws are applicable to both. In general it is assumed that the energy lost due to friction between the liquid and the sides of the channel varies as some function of the velocity, usually the square, and that the total energy passing any section of the stream differs from the energy passing any other section only by the loss of energy due to friction. The general expression for the flow of sewage would then be, h=(f)V n , in which h is the head or energy lost between any two sections, and V is the average velocity of flow between these sections. It is to be noted in this general expression that the quantity and rate of flow past all sections is assumed to be constant. This condition is known as steady flow. Problems are encountered in sewerage design which involve conditions of unsteady flow, and methods of solution of them have been developed based on modifications of this general expression. The average velocity of flow is computed by dividing the rate (quantity) of flow past any section by the cross-sectional area of the stream at that section. This does not represent the true velocity at any par- ticular point in the stream, as the velocity near the center is faster than that near the sides of the channel. The distribution of velocities in a closed circular channel is somewhat in the form of a paraboloid superimposed on a cylinder. The laws of flow are expressed as formulas the constants of which have been determined by experiment. It has been found that these constants depend on the character of the material 51 52 THE HYDRAULICS OF SEWERS forming the channel and the hydraulic radius. The hydraulic ladius is denned as the ratio of the cross-sectional area of the stream to the length of the wetted perimeter, or line of contact between the liquid and the channel, exclusive of the horizontal line between the air and the liquid. 35. Formulas. The loss of head due to friction caused by flow through circular pipes flowing full as expressed by Darcy is, in which h is the head lost due to friction in the distance /, V is the velocity of flow, g is the acceleration due to gravity, and / is a factor dependent on d and the material of which the pipe is made. A formula for / expressed by Darcy as the result of experiments on cast iron pipe is, in which d is the diameter in feet. In using the formula with this factor the units used must be feet and seconds. Another form of the same expression is known as the Chezy formula. It is an algebraic transformation of the Darcy formula, but in the form shown here, by the use of the hydraulic radius, it is made applicable to any shape of conduit either full or partly full. The Chezy formula is, V = C\/RS, in which R is the hydraulic radius, S the slope ratio of the hydraulic gradient, and C a factor similar to / in the Darcy formula. Kutter's formula was derived by the Swiss engineers, Gan- guillet and Kutter, as the result of a series of experimental observa- tions. It was introduced into the United States by Rudolph Hering and its derivation is given in Hering and Trautwine's translation of " The Flow of Water in Open Channels by Gan- guillet and Kutter." In English units it is, V = VRS, / FORMULAS 53 in which n is a factor expressing the character of the surface of the conduit and the other notation is as in the Chezy formula. V is the velocity in feet per second, S is the slope ratio, and R the hydraulic radius in feet. The values of n to be used in all cases are not agreed upon, but in general the values shown below are used in practice. VALUES OF n IN KUTTER'S FORMULA n CHARACTER OF THE MATERIALS . 009 Well-planed timber. 0.010 Neat cement or very smooth pipe. 0.012 Unplaned timber. Best concrete. 0.013 Smooth masonry or brickwork, or concrete sewers under ordinary conditions. 0.015 Vitrified pipe or ordinary brickwork. 0.017 Rubble masonry or rough brickwork. 0.020 035 / Smooth earth 050 } R u gh channels overgrown with grass. Kutter's formula is of general application to all classes of material and to all shapes of conduits. It is the most generally used for- mula in sewerage design. The cumbersomeness of Kutter's formula is caused somewhat by the attempt to allow for the effect of the low slopes of the Mississippi River experiments on the coefficients. The correct- ness of these experiments has not been well established and the 0028 slopes are so flat that the omission of the term -'^ will have o no appreciable effect on the value of V ordinarily used in sewer design. The difference between the value of V determined by the omission of this term and the value of V found by including it is less than 1 per cent for all slopes greater than 1 in 1,000 for 8 inch pipe (# = 0.167 feet). As the diameter of the pipe or the hydraulic radius of the channel increases up to a diameter of 13.02 feet (# = 3.28 feet), the difference becomes less and at this value of R there is no difference whether the slope is included or not. For larger pipes the difference increases slowly. For a 16 foot pipe (R = 4 feet) on a slope of 1 in 1,000 the difference is less than 0.2 per cent, and on a slope of 1 in 10,000 the difference is approximately 1 per cent. Flatter slopes than these are 54 THE HYDRAULICS OF SEWERS seldom used in sewer design, except for very large sewers where careful determinations of the hydraulic slope are necessary. It is therefore safe in sewer design to use Kutter's formula in the 002S modified form shown below in which the term ^ has been o omitted. n(V72+41.67n) Bazin's formula is in which a and j3 are constants for different classes of material. For cast-iron pipe a is 0.00007726 and (3 is 0,00000647. This formula is seldom used in sewerage design- Exponential formulas have been developed as the result of experiments which have demonstrated that V does not vary as the one half power of R and S but that the relation should be expressed as, V=CR P &, in which p and q are constants and C is a factor dependent on the character of the material. The various formulas coming under this classification have been given the names of the experi- menters proposing them. Examples of these formulas are: Flamant's, in English units, for new cast iron pipe, which is, and Lampe's for the same material which is, F=203.3# 694 S 555 . These formulas are useful only for the material to which they apply, but they can be used for conduits of any shape'. A. V. Saph and E. W. Schoder have shown l that the general formula for all materials lies between the limits, 1 Transactions of the American Society of Civil Engineers, Vol. 51, 1903, p. 11. SOLUTION OF FORMULAS 55 Hazen and Williams 7 formula is in the form, in which C is a factor dependent on the character of the material of the conduit. The values of C as given by Hazen and Williams are, C CHARACTER OF MATERIAL 95 Steel pipe under future conditions. (Riveted steel.) 100 Cast iron under ordinary future conditions and brick sewers in good condition. 110 New riveted steel, and cement pipe. 120 Smooth wood or masonry conduits under ordinary conditions. 130 Masonry conduits after some time and for very smooth pipes such as glass, brass, lead, etc., when old, and for new cast-iron pipe under ordinary conditions. This formula is of as general application as Kutter's formula and is easier of solution, but being more recently in the field and because of the ease of the solution of Kutter's formula by dia- grams it is not in such general use. Exponential formulas are used more in waterworks than in sewerage practice. Manning's formula is in the form, n in which n is the same as for Kutter's formula. Charts for the solution of Manning's formula are given in Eng. News-Record, Vol. 85, 1920, p. 837. 36. Solution of Formulas. The solution of even the simplest of these formulas, such as Flamant's, is laborious because of the exponents involved. Darcy's and Kutter's formulas are even more cumbersome because of the character of the coefficient. The labor involved in the solution of these formulas has resulted in the development of a number of diagrams and other short cuts. Since each formula involves three or more variables it cannot be represented by a single straight line on rectangular coordinate paper. The simplest form of diagram for the solution of three or more variables is the nomograph, an example of which is shown 56 THE HYDRAULICS OF SEWERS -48 3 -g 36.5 24 1.5- 2 - in Fig. 13 for the solution of Flamant's formula. A straight-edge placed on any two points of the scales of two different ver- tical lines will cross the other line at a point on the scale cor- responding to its correct value in the formula. Such a diagram is in common use for the solution of problems for the flow of water in cast-iron pipe. Fig. 14 has been prepared to simplify the solution of Hazen and Williams' formu- la. The scales of slope for different classes of material are shown on vertical lines of the slope line, these scales must be 0.00003 0.0001 0.001 0.01 O.I 10- FIG. 13. Diagram for the Solution of Flamant's Formula for the Flow of to tne Water in Cast-iron Pipe. For use projected horizontally on the slope line. The scales for other factors are shown on independent reference lines. For example let it be required to find the loss of head in a 12 inch pipe carrying 1 cubic foot per second when the coefficient of roughness is 100. . A straight-edge placed at 1.0 cubic feet per second on the quantity scale, and 12 inches on the diameter scale crosses the slope line at 0.00092 opposite the slope scale for c=100. It crosses the velocity line at 1,31 feet per second. Kutter's formula is the most commonly used for sewer design and has been generally accepted as a standard in spite of its cumbersomeness. Fig. 15 is a graphical solution of Kutter's formula for small pipes, and Fig. 16 for larger pipes. The dia- grams are drawn on the nomographic principle and give solutions for a wide range of materials, but they are specially prepared for the solution of problems in which n=.015. In their preparation the effect of the slope on the coefficient has been neglected. Fig. 17 is drawn on ordinary rectangular coordinate paper and can be used only for the solution of problems in which n=.015. Both diagrams are given for practice in the use of the different types. SOLUTION OF FORMULAS 57 - 10 48" -9 : 8 42" I 7 36" -6 33" 30" -5 : IT r4 24" 21" ,3 20" 18" 15" -I 10" 9" :- 9 \ 8 " Values of C 2S )0 0.8- 0.9- 1.0- 1.5- 2- c ? 5- \ \ X v\\ _ sj \ SX v - \ o ^sX - s |s x - \ - s^C \ - \ \ - ^ ~ x ~ \ \ 1 1 - \ x \ ^ \ } -^ ~i \ - \ V \ - V \ <0- \ fe D T \ \ X V X] c - v X ^ _ \ \ V \ X O - \ X s ^ u_- \ \ \ t \ - \ C - \ ^ ' \ \ N - 0) i i 0) 5 s 3 - 5 : Q- *~ o o - 05 4- \ N 0> \ \ \ \\ \ \ \ X^ \ \ X x i. > : \ ^ \ x\ ^ _ -0.7 _ 4- X 6 +_ - ^ J^ ^~ . c : y i_ ~ \ 0) C u_ " n* o - c \ ' ^ V \ - ^~ \ \ \ - u.o ,*j "3 4- - -04 o \- U-p Xy \ ^ \ - c *- \ \ 0) (0 j ! 4? L 0.3? <0 o \~\ \ x _ > 4- _ \ \ I \x x V \ 4.5- tr - \ \\ \ r s] o - \ \ S \ ^ : \ r 5. > \ S X \- s \ \ y ^ . -0.2 \ s \ \ ^ c c - S \ ^ \ ^_ \ 7 6- \ \ ^ - \ O . r \ v [^ ^ &5- \ "2. \ \ \^_ 7- \- \ . 7R- \ - _n i \ s a_ \~\ \ k N _ X X ^_ ^ i - FIG. 14. Diagram for the Solution of Hazen and Williams' Formula. 58 THE HYDRAULICS OF SEWERS Values of n \ S " {4T 1 " x ^ J * _ n x JU 7 X *^ ^ J \ ^ x 33 N, N 5 6 "X \ ^ "if}" \ 28" c \ S> ~ \ * 26" v ^ c i^ s - 24 fv v ^ c 4 . 99' 1 * X - ^ ^ L. U "V ^ ^ 7 A" "V ul/ * ^ ? Ift" \ s^ s^ . < \y ,C" .1C" ^* _o 0.9 o 3.8(0 *s "\ n? fc ^ * \ / - A * -6 L fifi "aj U.D QJ U 0.5 _5 -) s \ 34 c \ \ ^ >^ S -4" fe n^ -3 \ c* 02 a. * > 7 .000 1 .000? 1.0- r -I .0003 1 j .0004 4 .0005 ~ .0006 AA A" 15- p a.uuui J.0008 o 9 .001 ^ Lf> "ro D ' .002 LLJ C "to u 20~ cr -^ .003 ^ i LLJ T5 c | 2 .004 .005 C o (0 - .006 I/) _c CC J .007 2.5- o c QJ ^ .008- Q. c 0.1 . .01 t - u_ 1 t/> j c - 5 - 5 : - 04 ^ .05 2 .06 4.0 : ^ 07 ^ .08 i .1 4.5: i 2 5.0; fc j .3 5.5; i .4 6.0: ^ .5 ^_ 6 6.5 T _i 7 I 1 8 7.0- ^ 1.0 ; FIG. 15. Diagram for the Solution of Kutter's Formula. For values of n between 0.010 and 0.020. Specially arranged for = 0.015. Values of Q from G.I to 10 second-feet, SOLUTION OF FORMULAS 59 Values of n > - OslhO LT> onn i^ x ^ x ^ ?. L\J X "^ 1 9 Qrtrt ^ . X . R 5 1 fl* 00 . ^ x ^ 5 n s 17* s^ s^ 700 S^S^ ? ^ 16' j^ ^ v 1C' ^ iOO ^%^ ^ s 14* ! S 13' cno ^ ^> ^ I ^ 12' i [~ ir ^ 00 "x ^ _. p I I Al s r 1 IU "N S. Al ^ TAO ^ x j^ r ""N X 96" n 'x, 's s I s ^N ^ v B v ^ 90" i^ " QA" v^ ^ ^ s OT ""s T - 78' -H sj ^ ^ C^ 200 \ r - 7?' m rs s E ^ w > s 66 tff E 4- s ^^_ ? s 60" C Q; ^^ T E: ^^ N^ 54 36' ?n CD x " T^ s c/i ^ x i en L. ^ v N 3 7 A' ^~" OU Q. . * ! 4 ; 1 "^ ^ >' 27" 50 * s x r J s ^ ^r 7/1* o > tH 405 % J s ^b* V 7I ^ x K 'tl ?r\ ] 1 0* oU ^> N lo rtz I 1 ( 20 10 ~ UUI 3- -i 0002 -j 0003 4r J 0004 ] 2 0005 - r 0006 0007 o , ^ 0008 5r 2 001 " (0 or 1 e-i OJ 002 J C j 003 7-i ^ T3 J 004 j C o ^ 005 8- 4- ^ 006 CO o: -d 007 008 9 J CD 0- o_^ 01 _ 0) io j 10- o> U. C -j .02 II - z, j .03 12- 1 .04 13- Q.) .05 14- .06 .07 15- .08 16- .1 17- 18- 19- .2 20- .3 .4 .5 .6 I \ n FIG. 16. Diagram for the Solution of Kutter's Formula. For values of n between 0.010 and 0.020. Specially arranged for n = 0.015. Q from 10 to 1,000 second-feet. Values of 60 THE HYDRAULICS OF SEWERS 060-0 oeo'o OZO'O 090'0 OSO'O JOO'O 6000'0 8000'Q ZOOO'O 9000-Q SOOO'O USE OF DIAGRAMS 61 In Figs. 15 and 16 the diameter scales are varied for different values of the roughness coefficient n. The velocity scale is shown only for a value of n=.015. The velocity for other values of n can be determined by the method given in the following paragraphs. 37. Use of Diagrams. There are five factors in Kutter's formula: n, Q, V, d (or R), and S. If any three of these are given the other two can be determined, except when the three given are Q, F, and d. These three are related in the form Q=AV, which is inde- pendent of slope or the char- acter of the material. There Values of n. FIG. 18. Conversion Factors for Kutter's Formula. are only nine different com- binations possible with these five factors, which will be met in the solution of Kutter's formula. The solution of the problems by means of the diagrams is simple when the data given include n=.015. For other given values of n the solu- tion is more complicated. Results of the solution of types of each of the nine problems are given in Table 17 and the explanatory text below. // n is given and is equal to .015, the solution is simple. For example in Table 17 case 1, example 1; to be solved on Fig. 15. Place a straight-edge at 1.0 on the Q line and at 6 inches on the diameter line for n= .015. The slope and the velocity will be found at the intersection of the straight-edge with these respective scales. All problems in which n is given as .015 and the solution for which falls within the limits of Fig. 15 or 16 should be solved by placing a straight-edge on the two known scales and reading the two unknown results at the intersection of the straight-edge and the remaining scales. For example in case 1, example 2 find the intersection of the horizontal line representing Q=100 with the sloping 62 THE HYDRAULICS OF SEWERS diameter line representing d4S inches. The vertical slope line passing through this point represents S= .0065 and the sloping velocity line passing through this point represents 8.5 feet per second. In general problems in which n=.015, can be solved on Fig. 17 by finding the intersection of the two lines representing the given data, and reading the values of the remaining variables represented by the other two lines passing through this point. TABLE 17 SOLUTIONS OF PROBLEMS BY KUTTER'S FORMULA Ex- Givei i Foun d Case ample n Q V d S n Q V d S 1 1 1 2 0.015 .015 1.0 100.0 2.5 6 5.0 8.5 0.0575 .0065 1 1 2 3 4 1 .020 .020 015 1.0 100.0 5 6 48 0003 5.0 8.5 1 2 28 .13 .0125 2 2 010 5 0003 1 7 23 5 3 3 1 2 .015 018 18 18 .002 0008 40 2 2.25 1 1 4 1 015 2 ? 5 12 00475 4 5 2 1 .011 015 2.0 2.5 5 36 35 12 .0022 0038 6 1 018 5 001 185 80 7 7 8 9 1 2 1 1 3.0 50.0 6.0 2.5 4 ? 18 36 66 .002 .005 .003 00059 0.019 .012 .018 Oil 100 1.7 7.0 21 I/ n is given and is not equal to .015 the solution is not so simple. In Fig. 15 and 16 the diagram is so drawn that the position of the diameter scales for all values of n is fixed on the vertical " diameter " line. The scales of diameter change for each value of n. These scales of diameter are shown for each value of n from .010 to .020 on vertical lines to the left of the " diameter " line. For use, the proper diameter scale for any given value of n must be projected horizontally upon the vertical " diameter " line. The velocity can be determined on Fig. 15 and 16, only USE OF DIAGRAMS 63 when the diameter has been determined and then only when the diameter scale for n equal .015 is used, since the only scale shown for velocity is for n= .015. For example, in Case 1, Example 3 there are given n= .020, Q, and d. Find the intersection of the vertical line for n = . 020 with the sloping diameter line for d = 6 inches. Project the intersection horizontally to the right to the vertical "diameter" line. Place a straight-edge at this point and at Q = 1.0 on the quantity scale. The required value of S is read at the intersection of the straight- edge and the slope scale and is equal to 0.13. The inter- section of the straight-edge in this position with the velocity scale is not the required value of the velocity since the velocity scale is made out for n= .015 and not .020. It is necessary to change the position of the straight-edge so that it may lie on Q equal 1.0 and on d equal 6 inches for n equal .015. The value of V is shown in this position as 5 feet per second. The reverse process for Fig. 15 and 16 is illustrated by Case 4, Example 2 in which n= .011 and Q and V are also given. When Q and V are given the value of d is fixed independent of all other factors. Therefore the value of d can be read from the scale with n= .015 and is found to be 12 inches. Now find the value of d= 12 inches on the scale for n= .011 and project on to the "diameter" line. Place the straight-edge at this point and at Q = 2. The required slope is read as . 0022. Fig. 17 is prepared for the solution of problems in which n=.015 only. For problems in which n has some other value it is necessary to transform the data to equivalent conditions in which n=.015. This is done by means of the conversion factors shown in Fig. 18. The given slope or velocity is multiplied by the proper factor to convert from or to the value of n= .015, For example in Case 1, Example 4 there are given n= . 020, Q, and d. With Q and d given the value of V can be read from Fig. 17 without conversion. The correspond- ing value of S for n= .015 is .0065. It is now necessary to use the transformation diagram Fig. 18. The hydraulic radius of the given pipe is one foot. On Fig. 18 at the inter- section of the slope line for #=1.0 foot and n = . 020 the value of the factor is read as 1.92. Since the given n is for rougher material than that represented by n= .015 the required slope must be greater than forn= .015 to give the 64 THE HYDRAULICS OF SEWERS same velocity. It is therefore necessary to multiply . 0065 X 1 . 92 and the required slope is .0125. In Case 6, Example 1 there are given n= .018, d, and S, The remaining factors are to be solved by Fig. 17. Solve first as though n= .015 in order to find an approximate value of d or R. In this case it is evident that d is greater than 57 inches. The value of R is therefore about 1.25. Referring to Fig. 18 the conversion factor for the slope for n= .018 is about 1.52. Since the given slope for n= .018 is .001, for an equal velocity and for n= .015 the slope should be less. Therefore in reading Fig. 17 it is necessary 001 to use a slope of ^ =^ = .00066. The diameter is found to 1 . oZ be about 80 inches. Since this is nearer to the correct diameter the value of the conversion factor must be cor- rected for this approximation. The hydraulic radius for an 80 inch pipe is 1.67 feet, and the conversion factor from Fig. 18 is about 1.48. The slope for ft =.015 should be 001 therefore j-^=. 000675 and from Fig. 17 the required diameter and quantity are read as 80 inches and 185 second feet, respectively, // n is not given but must be solved for, the solution on Fig. 15 and 16 is relatively simple. The desired value of n is read at the intersection of the sloping diameter line representing the known diameter and the horizontal projection of the intersection of the straight-edge with the vertical " diameter " line. For example in Case 7, Example 1 there are given Q, d, and S. Lay the straight-edge on the given values of Q = 3 and S= .002. At the point where the straight-edge crosses the vertical "diameter" line project a horizontal line to the sloping diameter line for d=18 inches. The vertical line passing through this point represents a value of n= .019. In order to find the value of V lay the straight- edge on Q = 3 and d= 18 inches for n= .015. The value of V is read as 1.7. A slightly different condition is illustrated in the solu- tion of Case 8, Example 1 in which Q, V and S are given. Determine first the value of d as though n= .015. Then proceed to determine n as in the preceding examples. The solution for an unknown value of n on Fig. 17 is not so simple. It must be determined by working backwards from the conversion factor. FLOW IN CIRCULAR PIPES PARTLY FULL 65 For example in Case 7, Example 2 there are given Q, d, and S. The value of V is read directly as though n = .015 as 7 feet per second. The value of S read for n= .015 is is .0075. But the given slope is .005. Since the given slope is flatter than that for n= .015 the conversion factor 005 is less than unity and is therefore -^yr= = . 67. With this value of the conversion factor and the value of R given as 0.75 the value of n is read from Fig. 18 as slightly greater than .012. 38. Flow in Circular Pipes Partly Full. The preceding examples have involved the flow in circular pipes completely filled. The same methods of solution can be used for pipes flowing partly full except that the hydraulic radius of the wetted section is used instead of the diameter of the pipe. Diagrams are used to save labor in finding the hydraulic radius and the other hydraulic elements of conduits flowing partly full. The hydraulic elements of a conduit for any depth of flow are : (a) The hydraulic radius, (6) the area, (c) the velocity of flow, and (d) the quantity or rate of discharge. The velocity and quantity when partly full as expressed in terms of the velocity and quantity when full as calculated by Kutter's formula will vary slightly with different diameters, slopes and coefficients of roughness. The other elements are constant for all conditions for the same type of cross-section. The hydraulic elements for all depths of a circular section for two different diameters and slopes are shown in Fig. 19. The differences between the velocity and quantity under the different conditions are shown to be slight, and in practice allowance is seldom made for this discrepancy. In the solution of a problem involving part full flow in a cir- cular conduit the method followed is to solve the problem as though it were for full flow conditions and then to convert to partial flow conditions by means of Fig. 19, or to convert from partial flow conditions to full flow conditions and solve as in the preceding section. For example let it be required to determine the quantity of flow in a 12-inch diameter pipe with n= .015 when on a slope of . 005 and the depth of flow is 3 inches. First find the quantity for full flow. From Fig. 15 this is 2.0 cubic feet per second. The depth of flow of 3 inches is one-fourth 66 THE HYDRAULICS OF SEWERS or 0.25 of the full depth of 12 inches. From Fig. 19, run- ning horizontally on the 0.25 depth line to meet the quantity curve, the proportionate quantity at this depth is found to be on the 0.13 vertical line, and the quantity of flow is therefore 2 X0.13 = 0.26 cubic feet per second. O.t 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 Hydraulic Elements in Terms of Hydraulic Elements for Full Section. FIG. 19. Hydraulic Elements of Circular Sections. s = .0004 d = 12' 0" d= I'O" n = .015 n = .013 Another problem, involving the reversal of this process is illustrated by the following example: Let it be required to determine the diameter and full capacity of a vitrified pipe sewer on a grade of 0.002 if the velocity of flow is 3.0 feet per second when the sewer is discharging at 30 per cent of its full capacity, the depth of flow being 12 inches. From Fig. 19 the depth of flow when the sewer is carrying 30 per cent of its full capacity is . 38 of its full depth. Since the partial depth is 12 inches 12 the full diameter is =31.6 inches. The velocity of U . oo flow at 38 per cent depth is 86 per cent of the full velocity. Since the velocity given is 3.0 feet per second, the full 3 velocity is -^ = 3.5 feet per second. With a full ve- locity of 3.5 feet per second and a diameter of 31.6 inches from Fig. 16 the full capacity of the sewer is 18 cubic feet per second. SECTIONS OTHER THAN CIRCULAR 67 39. Sections Other than Circular. The ordinary shape used for small sewers is circular. The difficulty of constructing large sewers in a circular shape, special conditions of construction such as small head room, soft foundations, etc., or widely fluctuating conditions of flow have led to the development of other shapes. For conduits flowing full at all times a circular section will carry more water with the same loss of head than any other section under the same conditions. In any section the smaller the flow the slower the velocity, an undesirable condition. The ideal section for fluctuating flows would be one that would give the same velocity of flow for all quantities. Such a section is yet to be developed. Sections have been developed that will give rela- tively higher velocities for small quantities of flow than are given by a circular section. The best known of these sections is the egg shape, the proportions and hydraulic elements of which are shown in Fig. 20. Other shapes that have the same property, but which were not developed for the same purpose are the rect- angular, the U-shape, and the section with a cunette. The egg- shaped section has been more widely used than any other special section. It is, however, more difficult and expensive to build under certain conditions, and has a smaller capacity when full than a circular sewer of the same area of cross-section. Various sections are illustrated in Fig. 22 and 23. The U-shaped section is suitable where the cover is small, or close under obstructions where a flat top is desirable and the fluctuations of flow are so great as to make advantageous a special shape to increase the velocity of low flows. The proportions of a U-shaped section are shown in Fig. 23 (6). Other sections used for the same purpose are the semicircular and special forms of the rectangular section. The proportions and the hydraulic elements of the square- shaped section are shown in Fig. 21. This is useful under low heads where a flat roof is required to carry heavy loads, and the fluctuations of flow are not large. Sections with cunettes have not been standardized. A cunette is a small channel in the bottom of a sewer to concentrate the low flows, as shown in Fig. 22 (7). A cunette can be used in any shape of sewer. Sections developed mainly because of the greater ease of con- struction under certain conditions are the basket handle, the gothic, THE HYDRAULICS OF SEWERS O.I 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 I.I 1.2 Hyoraulic Elements in Terms of Hydraulic Elements for Full Section FIG. 20. Hydraulic Elements of an Egg-shaped Section. d = 6'0" s = .00065 n = .015 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 Hydraulic Elements in Terms of Hydraulic Elements for Full Section. FIG. 21. Hydraulic Elements of a Square Section. d = 10' 0" s = .0004 n = .015 SECTIONS OTHER THAN CIRCULAR the catenary, and the horse shoe. Some of these shapes are shown in Fig. 22 and 23. They are suitable for large sewers on soft foundations, where it is desirable to build the sewer in three portions, such as, invert, side walls, and arch. They are also suitable for construction in tunnels where the shape of the sewer conforms to the shape of the timbering, or in open cut work where the shape of the forms are easier to support. Problems of flow in all sections can be solved by determining the hydraulic radius involved, and substituting directly in the desired formula, or by the use of one of the diagrams after con- verting to the equivalent circular diameter. The determina- tion of the hydraulic radius of these special sections is laborious, and hence other less difficult methods are followed. Problems are more commonly solved by converting the given data into an equivalent circular sewer, solving for the elements of this cir- cular sewer and then reconverting into the original terms, or by working in the other direction. The hydraulic elements of vari- ous sections when full are given in Table 18. TABLE 18 HYDRAULIC ELEMENTS OF SEWER SECTIONS. SEWERS FLOWING FULL Vert. Area Dia. D in Hy- in Terms draulic Section Terms Vertical Diameter Squared Radius in terms of Vertical Din D of Dia. d of Equiv- alent Source L> 2 .L/ It* . i ' . Circular Section Circular . 7854 0.250 1.000 Egg 0.5150 . 1931 1.295 Eng. Record, Vol. 72: 608 Ovoid . 5650 .2070 1.208 Eng. Record, Vol. 72: 608 Semi-elliptical 0.8176 .2487 1.041 Eng. News, Vol. 71: 552 Catenary . 6625 .2237 1.1175 Eng. Record, Vol. 72: 608 Horseshoe 0.8472 .2536 0.985 Eng. Record, Vol. 72: 608 Basket handle. . 0.8313 .2553 0.979 Eng. Record, Vol. 72. 608 Rectangular 1.3125 .2865 .7968 Hydraulic D^ms. and Tbls. Garrett Square (3 sides wet) . 1.0000 .333 .7500 Eng. Record, Vol. 72: 608 Square (4 sides wet) . 1.0000 .250 1.0000 Eng Record, Vol. 72: 608 1 70 THE HYDRAULICS OF SEWERS 7*- V_ /-*_[_ _r - ^ ...... ^^^.^ U <- 20'- 1. Standard Egg-shaped Section, North 2. Rectangular Section, Omaha, Nebraska, Shore Intercepter, Chicago, Illinois. Eng. Contracting, Vol. 46, p. 49. 3. Trench in firm 4. Trench in ground. Rock. NOTE Underdrains and Wedges to be used only when Ordered by the Engineer. ^ fact Brick 7. Brick and Concrete Sewer showing cunette. Concrete 6 'ravel 'or r / j i Broken Stone.-''' Plank , Filling }< 13-10"- 5. Soft Founda- 6. Wet 8. Brick and Concrete Sewer, Evanston, tion. ground. 111., Eng. Contracting, Vol. 46, p. 227. FIG. 22. SECTIONS OTHER THAN CIRCULAR 71 flLjJM- ! *t1 i i U '.rt '. '. .AandB Covers. and Bosses tobeJemittedon [ andC CovepSCoyer C to be used on all Sidewalks and jj. Crown elsewhere as di reefed. x> -jj ^Frame and Cover asphalf 1 - " \ed.Corruga- FIG. 31. Adjustable Manhole Frame and Cover. hole covers should be so marked that the sanitary sewer can be distinguished from the storm water sewer, and both from the telephone conduit, etc. Iron steps are set into the walls of the manhole about 15 inches apart vertically to allow entrance and exit to and from the manhole. Galvanized iron is preferable to unprotected metal as the action of rust is particularly rapid in the moist air of the sewer. 104 APPURTENANCES One type of these manhole steps is shown in Fig. 27. The steps should have a firm grip in the wall as a loose step is a source of danger. 57. Lampholes. A lamphole is an opening from the surface of the ground into a sewer, large enough to permit the lowering of a lantern into the sewer. Lampholes are used in the place of manholes to permit the inspec- tion or the flushing of sewers, and to avoid the expense of a manhole. They are located from 300 to 400 feet from the nearest manhole in such a manner that a lamp lowered in the lamp hole can be seen from the two nearest man- holes. Lampholes should be con- structed of 8- to 12-inch tile or cast-iron pipe. The lower section should be a cast iron T on a firm foundation, but if constructed of tile it should be reinforced with concrete to take up the weight of the shaft. The details of the Baltimore standard lamphole are shown in Fig. 32. Lampholes are not com- monly used on sewerage sys- tems on account of their lack of real usefulness and the troubles encountered by breaking of the pipe below the shaft. 58. Street Inlets. A street inlet is an opening in the gutter through which storm water gains access to the sewer. The types used in different cities vary widely. Details of an inlet in success- ful use are shown in Fig. 33. The figure shows also a common form of connection to the sewer. A water-seal trap is sometimes used to prevent the escape of odors from the sewer. Care must be taken in design that such traps do not freeze in winter nor dry FIG. 32. Baltimore Standard Lamphole. STREET INLETS 105 _ ?'5 " il * 1 Tk r* n] L_ _|j (7^ *n i^r .i ^ V [7- TT "c f-i* I 1 *Q 1* I 1 (J F* n j i 1 tz -dJ I ^ out in summer, although it is not always possible to prevent these contingencies. The important features to be observed in the design of a street inlet are: height and length of opening, character of grating, and location. The general location of inlets is discussed in Chapter V. The clear height of opening commonly used is from 5 to 6 inches, with a clear length of 24 to 30 inches or longer. Inlets of this size have given satisfaction on paved streets with moderate slopes, where the drainage area is not greater than 10,000 to 12,000 square feet of pavement. W. W. Horner states: 1 The St. Louis type of inlet " old " style was a vertical opening in the curb 8 inches high and 4 feet in length with a horizontal bar mak- ing the net opening about 5 inches. It has a broad sill extending under the sidewalk. The " new " style inlet is 4^ feet long with a clear opening of 6 inches and no bar. The sill is done away with and the opening drops down directly from the curb. Tests were made of the capacity of this inlet on pavements on different slopes with sumps of depths varying from to 6 inches FIG. 33. Details of an Untrapped in front of the inlet, extend- Street Inlet, without Catch-Basin, ing out 3 feet from the gutter, and returning to the elevation of the gutter at a slope of 3 inches to the foot. The results of these tests are shown in Table 22. The capacity of the inlet is expressed as the amount of water entering just before some water begins to lap past. If a large amount of water is allowed to flow past much more water will enter the inlet thus furnishing a factor of safety for large storms. It was noted that by beginning the rise in the pavement about opposite the 1 Municipal and County Engineering, October, 1909. k - 26" ol 106 APPURTENANCES middle of the inlet the capacity of the inlet was increased from 20 to 50 per cent. TABLE 22 CAPACITIES OF ST. Louis STREET INLETS From tests by W. W. Horner. Cubic feet per second Slope in Per Ct. 0.42 1.5 2.85 4.5 Depth of Sump, Inches 0.0 2 4 6 0. 2 4 6 2 4 6 2 4 6 Capacity, old style 1 27 03 25 78 1 49 Capacity, new style 0.1 0.5 1.5 2.5 0.08 0.4 1.1 2.1 0.03 0.28 0.87 1.62 0.02 0.15 0.45 1.0 Gratings with horizontal bars will admit more water than gratings with vertical bars, but they will also admit more rubbish such as sticks, papers, leaves, etc., which serve to clog the sewers. Vertical barred gratings and gratings in the bottom of the gutter clog more quickly than other types. In the selection of the type of grating to be used a decision must be made as to whether it is more desirable to clean the sewer or catch-basin, or to flood the street as a result of clogged inlets. Where catch-basins are used or the sewers are large, horizontal bars are more satisfactory. The openings between bars should be small enough to prevent the entrance of a horse's hoof or objects of sufficient size to clog the sewer. Four inches in the clear for vertical openings and 6 inches for horizontal openings are reasonable sizes. The location of the inlets at the intersection of the two curb lines at a corner results in a lower first cost but on heavily traveled streets this may result in a higher maintenance cost than for other locations because of the concentration of traffic at street corners, hammering the inlet casting out of shape or position. Vehicles making short turns will tend to climb the curb and will intensify the wear upon the inlet. These objections can be overcome by the use of two inlets at each corner, set back far enough from the curb intersection to avoid interference with the cross-walks. This also makes it possible to raise the cross-walks without the use of gutters under them. The size of the pipe from the inlet to the catch-basin or sewer should be large enough to care for all of the water which may enter CATCH-BASINS 107 the inlet. As the capacity of the inlet is seldom known with accu- racy and the capacity of the pipe is difficult of determination, it has become customary to use a 10-inch or a 12-inch connecting pipe for each ordinary independent inlet. 59. Catch-basins. Catch-basins are used to interrupt the velocity of sewage before entering the sewer, causing the deposi- tion of suspended grit and sludge and the detention of floating rubbish which might enter and clog the sewer. A separate catch- Street Inlet FIG. 34. CATCH-BASIN. Outlets are not always trapped. basin may be used for each inlet, or to save expense, the pipes from several inlets may discharge into one catch-basin. The types in successful use are extremely varied, but the dis- tinguishing feature of all is an outlet located above the floor of the basin. A common form of catch-basin is shown in Fig. 34. It is constructed similar to a manhole with a diameter of about 4 or 4^ feet and a depth of retained water from 3 to 4 feet. Catch- basins of this size will care for the sewage from the inlets at the four corners of a street intersection, each draining a city block. 108 APPURTENANCES In unusual situations it may be necessary to install a larger basin, but too large a catch-basin is less desirable than one which is too small, as the former stinks and the latter is useless. Traps are sometimes used to prevent the escape of odors from the sewer into the street, but odors are often created in the catch-basins themselves. Some engineers arrange the trap so that it can be opened for observation down the sewer as in Fig. 34, thus com- bining the advantages of a manhole with the catch-basin. The use of catch-basins is objectionable because: they furnish a breeding place for mosquitoes and other flying insects; the septic action in them produces offensive odors; if on a combined sewer they permit the escape of offensive odors in dry weather when the water seal in the trap has evaporated; and the freezing of the water seal in the trap prevents the entrance of water to the sewer. The sole advantage lies in the prevention of the clogging of the sewers, but this may be sufficient to overbalance all of the disadvantages. In general catch-basins should be provided on paved streets which are cleaned by flushing the material into the sewers, or where the drainage is from an unim- proved or macadamized street, sandy country, or into sewers in which the velocity of flow is less than 2 feet per second. 60. Grease Traps. The presence of grease in sewers results in the formation of incrustations which are difficult to remove and which cause a material loss in the capacity of the sewer. The presence of oil and gasoline has re- sulted in violent and destructive ex- plosions as is described in Chapter XII. A type of grease trap 'used on the drains from hotels, restaurants, or other large grease producing indus- FIG. 35.-Diagrammatic Sec- tries . is shown in Yi %' 35 ' The tra P tion through a Grease Trap. i g similar to a catch-basin except that it is too small for a man to enter, and the outlet is necessarily trapped in order to pre- vent the escape of grease. The details of a gasoline and oil separator approved by the New York City Fire Department are shown in Fig. 36. 1 1 "Cleaning and Flushing Sewers. " Journal of the Association of Engineer- ing Societies, Vol. 33, 1904, p. 212. FLUSH-TANKS 109 fW. 4 Clean-out FIG. 36. Gasoline and Oil Separator. 61. Flush-Tanks. These are devices to hold water used in flushing sewers. They are required only on sanitary and com- bined sewers. Their use tends to prevent the clogging of sewers laid on flat grades and permits flatter grades in construction than could otherwise be adopt- ed. Flush-tanks may be oper- ated either by hand or auto- matically. Automatic operation is more common than hand operation. The hand-operated tanks are similar to manholes so arranged that the inlet and outlet sewers can be plugged while the manhole or tank is being filled with water either from a hose or a special service connection. When sufficient water has been accumulated the outlet is opened and the sewer is flushed by the rush of water. A sluice gate, flap valve, or a specially fitted board is sufficient to fit over the mouth of the inlet and outlet during the filling of the tank. Such an arrangement has the advantage of being cheap, simple, and satisfactory, though somewhat crude. In some cases water is run into the tank at the same rate that it is discharged through the open outlet, maintaining a depth of 4 or 5 feet in the tank until the water passing the manhole below runs clean. The volume of water required by this method is large. Flushing water under a relatively high head is sometimes obtained by the use of tank wagons which are quickly emptied into the sewer through a canvas pipe dropped down a manhole. In all such cases if not well constructed the manhole is subject to caving due to the rush of water around the outlet. Precautions should be taken to minimize this danger by limiting the depth of water which may be accumulated. This can be done by constructing an overflow at a height of 4 or 5 feet above the bottom of the man- hole, discharging into the sewer through an outside drain. Automatic flush-tanks are constructed similar to a manhole, but special care should be taken to make them water-tight. The 110 APPURTENANCES Regu/a- apparatus for providing the automatic discharge may operate either with or without moving parts, the latter being preferable as they require less attention and are not so liable to get out of order. An automatic flush-tank of the Miller type is shown in Fig. 37. It is a patented device manufactured by the Pacific Flush Tank Company. The small pipe at the left is a service connection to the water main. Water is allowed to flow continuously into the tank at such a rate as to fill it in the required interval between dis- charges. The tanks are dis- charged as nearly once a day as it is practicable to regulate them. The rate of flow into the tank is determined by trial and varies to some extent with the water pressure. The regu- lator shown in the figure is desirable as the continuous flow through the ordinary cock soon wears it away. Some waters will cause deposits to form in the small passages of the cocks or regulators, thus cutting off the flow. The tank operates as follows: when the water rising in the tank reaches the bottom of the bell, air is trapped in the bell and prevented from escaping through the main trap by the water at A . As the water continues to rise in the tank the air in the bell is compressed, the water level at A is driven down and water trickles from the siphon at C. The height of the water in the tank above the level of the water in the bell is equal at all times to the height of C above the lowering position of A. When A reaches the position of B a small amount of air is released through the short leg of the trap and a corresponding volume of water enters the bell. The head of water above the bell then becomes greater than the head of water in the short leg of the trap, which results in the discharge of all of the air in the long leg of the trap and the rapid discharge of the water in the tank through the siphon. The discharge is continued until the siphonic action is broken by the admission of air when the water level in the tank is lowered FIG. 37. Automatic Flush-Tank. Pacific Flush Tank Co. FLUSH-TANKS 111 to the bottom of the bell. The size of the siphons is fixed by the diameter of the leg of the siphon. Table 23 shows the capacity and size of sewers for which the different sizes of siphons are recommended by the manufacturers. 1 TABLE 23 SIZES OF SIPHONS TO BE USED WITH AUTOMATIC FLUSH-TANKS Diameter rf Diameter of Tank Total Discharge Average Rate Diameter of Height of the Siphon at the Discharge for One Flush of Discharge Sewer Discharge Line above in Inches Line in Feet in Gallons in Sec .-ft. Inches the Edge of the Bell 4 3 60 0.35 4 to 6 1 ft. 2 in. 5 3 100 0.73 6 to 8 1 ft. 11 in. 6 4 240 1.0 8 to 10 2 ft. 6 in. 8 4 280 2.12 12 to 15 2 ft. 11 in. When flush-tanks are placed at the upper end of laterals provision should be made for inspecting and cleaning the sewer by the construction of a separate manhole, or by combining the features of a manhole and a flush-tank in the same structure. Such a combination is shown in Fig. 38 from a design by Alex- ander Potter. Except under unusual conditions flush-tanks are used only on separate sewers. They should be placed at the upper end of laterals in which the velocity of flow when full is less than 2 to 4 feet per second. The capacity of the tank or the volume of the dose is dependent on the diameter and slope of the sewer. The most effective flush is obtained by a volume of water traveling at a high velocity and completely filling the sewer. A .large volume allowed to run slowly through the sewer will have but little if any flushing action. Data on the quantity of flushing water needed are given in Table 24. 2 As the result of a series of experiments conducted by Prof. H. N. Ogden on the flushing of 1 Notes on the Design and Principles of Sewage Siphons, Eng. News-Record, Vol.85, 1920, p. 1041. 2 From A. E. Phillips, Trans. Am. Society of Municipal Improvements, 1898, p. 70. 112 APPURTENANCES v////n\ i i i i i i i- WS//A ?W\ ' ' ' ' ' ' W$fe: m 3 h Wafer line -4JP, ' J , ' , ' , ' , ' , ' , ' M^-^f,. fli. 1. 1 j ' i i I I jj ItejftrV ' Podding Trough- Floor RemovableCap Sectional Plan. FIG. 38. Automatic Flush-Tank and Manhole. Miller-Potter Design. Pacific Flush Tank Co. TABLE 24 GALLONS OF WATER NEEDED FOR FLUSHING SEWERS Diameter of Sewer in Inches slope 8 10 12 0.005 80 90 100 .0075 55 65 80 .01 45 55 70 .02 20 30 35 .03 15 20 24 SIPHONS 113 sewers, 1 the conclusion was reached that the effect of a flush of about 300 gallons in an 8-inch sewer on a grade less than 1 per cent would not be effective beyond 800 to 1,000 feet, but that on steeper grades much smaller quantities of water would produce equally good results. Engineers do not agree upon the advisability of the use of automatic flush-tanks, some believing that they are a needless expense that can be avoided by hand flushing, and others feeling that a flush-tank should be placed at the upper end of every lateral. These diverse opinions are the result of different experiences in different cities. 62. Siphons. There are two forms of siphons used in sewerage practice, a true siphon and an inverted siphon. A true siphon is a bent tube through which liquid will flow at a pressure less than atmospheric, first upwards and then downwards, entering and leaving at atmospheric pressure. An inverted siphon is a bent tube through which liquid will flow at a pressure greater than atmospheric first downwards and then upwards, entering and leaving at atmospheric pressure. In sewerage practice the word siphon refers to an inverted siphon unless otherwise qualified. Siphons, both true and inverted, are used in sewerage systems to pass above or below obstacles. True siphons are seldom used as they must be kept constantly filled with liquid. 2 Accumulated gas must be removed in order to prevent the breaking of the siphon which results in the cessation of flow. By the breaking of a true siphon is meant the stoppage of siphonic action due to the accumulation of air or gas at the peak of the siphon. Since the rate of flow of sewage fluc- tuates widely it is extremely difficult to control the flow so that a true siphon may be completely filled with liquid at all times. In the design of inverted siphons care must be taken to pre- vent sedimentation, and to permit inspection and cleaning. Sedimentation is prevented by maintaining a velocity greater than a fixed minimum, usually taken at about 2 feet per second. This minimum is attained by providing a number of channels. The smallest channel is designed to convey the least expected flow at the minimum velocity. Each of the other channels is made as small as possible, within the limits of economy and sim- 1 Trans. Am. Society of Civil Engineers, Vol. 15, 1886. 2 True Siphon at East Providence, Eng. News-Record, Vol. 85, 1920, p. 862. 114 APPURTENANCES plicity, in order that the minimum velocity shall be exceeded quickly after flow has commenced in them. The last channel or channels to be filled are made somewhat larger, because the sewage conveyed in them contains less settleable matter than is contained in the more concentrated dry weather flow. The type of siphon used in New York to pass under the subway is shown in Fig. 39. Note should be taken of the clean-out manhole provided on the 14-inch pipe. The other pipes are large enough for a man to enter and clean. Old 4'-6"Ct'rcularl?6tnf.Concreie 4-/Ox3 L 6" P M-fyP (Storm)Pipe^ Sewer Flout -Cleanout Chamber Cleanout Manhole Section A-A. 2 t 4-'-6"(Storm) Pipes-' Longitudinal Section , /4"CIP>'pe(DryWea- pPh Section B-B. FIG. 39. Sewer Siphon under New York Subway. Eng. News Vol. 76, p. 443. The computations involved in the design of a siphon are illustrated in the following example, in which it is desired to con- struct a siphon to pass under the railway cut shown in Fig. 40. The first step is to determine the limiting diameter and slope of the smallest pipe in the siphon. One-sixth of the capacity of the 6-foot approach sewer or 19 cubic feet per second will be assumed as the minimum flow. The diameter of the pipe necessary to carry 19 cubic feet per second at a velocity of 2 feet per second is 42 inches. The hydraulic gradient should have a slope of 0.0005 if the material used has a roughness coefficient of .015. This is ths minimum permissible slope of the siphon. The selection of a steeper slope will necessitate the laying of the sewer at a greater depth, and will permit the use of smaller pipes for the siphon. SIPHONS 115 The selection of the exact slope must then be based on judgment with the minimum limitation above placed. The slope will be arbitrarily selected as 0.001, the same as that of the approach sewer. The diameter of the dry weather pipe will therefore be 36 inches, with a capacity of 18 second-feet, which is approximately the assumed dry-weather flow. The velocity of flow will be 2.5 feet per second. The length of flow along the siphon is 150 feet. The next step should be the determination of the elevation at the lower end of the 36-inch pipe. This is done by multiplying 1 Vertical Cross Secfion 60 Sewer 42. Sewer 36 " Sewer Plan under Retaining Wall FIG. 40. Diagram for the Design of an Inverted Siphon. the assumed grade by the equivalent length of straight pipe, and subtracting the product from the elevation at the upper end. The length of straight pipe which will give the same loss of head as the siphon is called the equivalent pipe. It is determined as follows : First, determine the head loss at entrance. This will vary between nothing and one velocity head, dependent on the arrange- ment at the entrance. 1 The length of straight pipe which will 1 "The Effect of Mouthpieces on The Flow of Water Through a Sub- merged Short Pipe," by F. B. Seely. Bulletin No. 96, 1917, of the Eng'g. Experiment Station of the University of Illinois. 116 APPURTENANCES give this same loss can be computed from the expression 1=-^, using for S the assumed slope of the hydraulic gradient. Second, determine the head loss due to the bends. This is determined from the expression A=^ d2g in which /i = the head loss in the bend; Z = the length of the bend; d = the diameter of the pipe ; v = the average velocity of flow ; gr = the acceleration due to gravity; /=a factor dependent on the radius (R) of the bend and d. The relation between /, R, and d, for 90 bends is shown as follows: 1 R/d 24 16 10 6 4 2.4 / 0.036 0.037 0.047 0.060 0.062 0.072 After the head loss has been determined, the equivalent length of straight pipe is determined as above. Third. The equivalent length of pipe will be the sum of the actual length of pipe and the equivalent lengths as found above. In the problem in hand the head lost at the entrance will be assumed as one-third of a velocity head, or 0.0324 foot. With the assumed slope of 0.001 this is equivalent to 32 feet of pipe. The radius of the bend is about 20 feet and the length for a 45 central angle is about 16 feet. The head loss for this angle will probably be a little more than one-half that for a 90 angle. The V 2 expression will therefore be taken as about 0.2 5 and for two bends is equivalent to about 40 feet of pipe. The equivalent length of pipe is therefore 150+32+40 = 222 feet. The elevation at the lower end should therefore be : the elevation at the upper end, 92.07-222X.001 = 91.85. The diameters of the remaining pipes in the siphon are determined so that the sewage in the approach sewer is backed up as little as is consistent with good judgment before each pipe comes into action. This is done satisfactorily by a method of 1 Trans. Am. Society of Civil Engineers, Vol. 49, 1902. REGULATORS 117 cut and try. Let it be assumed that the siphon will be composed of three pipes: the dry-weather pipe taking 18 second-feet, the second pipe taking 28 second-feet, and the third pipe taking the remaining 70 second-feet. The diameters of the two larger pipes on the assumed slope of 0.001 will therefore be 42 inches and 60 inches respectively. Other combinations might be used which would be equally satisfactory. There are many methods by which the sewage can be diverted into the different channels of the siphon. For example, the openings into the different pipes may be placed at the same elevation, and the sewage allowed to enter them in turn through automatically or hand-controlled gates, or in another method of control the openings may be placed at such elevations that when the capacity of one pipe has been exceeded the sewage will flow into the next largest pipe as shown in Fig. 40. The outlets from the different pipes are ordinarily placed at the same elevation, thus leaving each pipe standing full of sewage. Stop planks should be provided at the outlet in order that the pipes may be pumped out for cleaning. The objection to this arrangement is that the larger pipes may operate at a velocity less than 2 feet per second, and they will be standing full of sewage which might become septic. However, as they will take nothing but the storm flow near the top of the sewer no difficulty should be encountered from sedimentation in them, and all are large enough for a man to enter for inspection or cleaning. 63. Regulators. Regulators are commonly used to divert the direction of flow of sewage in order to prevent the overcharging of a sewer or to regulate the flow to a treatment plant. Sewer regulators are of two types, those with moving parts and those without moving parts. An example of the moving part type is shown in Fig. 41. In this type as the sewage rises the float closes the gate to the inlet sewer, thus preventing the entrance of sewage under head from the larger sewer. There are many variations in the details of float-controlled regulators, but the principle of opera- tion is similar in all. These regulators can be adjusted to fix the maximum rate of flow to a relief channel or sewage treatment plant, or during times of storm to cut off the outlet to the dry- weather channel. Another form of the moving part type is shown in Fig. 42. 1 It has been used extensively by the Milwaukee 1 Described by W. L. Stevenson before the Boston Society of Civil Engi- neers in 1916 . 118 APPURTENANCES Sewerage Commission. In its operation the dry-weather flow is diverted by the dam into the intercepter. It passes under the movable gate on its way to the treatment plant. As the flow increases the dam is overtopped and flood waters are discharged down the storm chan- nel. The movable gate is hung on a pivot placed below center. As the water rises in the intercepter, the Copper Float pressure against the upper portion of the gate becomes greater than that against the FIG. 41. Coffin Sewer Regulator. lower portion, and the gate closes. An opening is left at the bottom to allow an amount of sewage equal to the dry-weather flow to escape beneath the gate to prevent clogging or sedimentation in the intercepter channel. Objections to all moving part regulators are their need of attention and liability to become clogged. Weight Direct/on of Flow -Relief Outlet -Dam Regulator Gate-. - StormSewer- Longitudinal Section - Dry Weather- -Storm Flow- Transverse Sections through Regulator. FIG. 42. Moving Part Regulator without Float. The overflow weir and the leaping weir have no moving parts and are used for the regulation of the flow in sewers. A leaping weir is formed by a gap in the invert of a sewer through which the dry-weather flow will fall and over which a portion or all of the storm flow will leap. One form of leaping weir is shown in Fig. 43. An overflow weir is formed by an opening in the side of a sewer high enough to permit the discharge of excess flow into a relief channel. A weir at San Francisco is shown in Fig. 44. A series of tests were run on leaping weirs and overflow weirs in the hydraulic laboratory of the University of Illinois. The type of REGULATORS 119 leaping weir tested was formed by the smooth spigot end of a stand- ard vitrified sewer pipe. The overflow weirs were formed by a Not more than 3ft -> J-IOorIZ Iron Grating.^ -Brick Cast Iron Grating ~7 Section of Inlet. Iron Casting to here \ , Slot Detail not to Scab / Longitudinal Section., ^ ; ! '[ T|l s ' ^s! 3-SS r S i * 2" Plan of Inlet. FIG. 43. Leaping Weir at Danville, Illinois. x - . Section through Hoof Showing Reinforcement under Manhole. Sectional Plan. Section A-A. Section B-B. Section C-G. FIG. 44. Overflow Weir at San Francisco. Eng. News, Vol. 73, p. 307. steel knife edge in the side of the pipe parallel to its axis as shown in Fig. 45. Tests were made in 18-inch and 24-inch pipes on various slopes from 0.018 to 0.005, for both leaping weirs and overflow 120 APPURTENANCES weirs. The overflow weirs were varied in length from 16 inches to 42 inches and were placed at various heights from 25 per cent to 50 per cent of the diameter above the invert of the sewer. As the result of the observations the following formulas were developed. For the leaping weir the expressions for the coordi- nates of the curve of the surfaces of the falling stream, are : For the outside surface x = For the inside surface x = Q FIG. 45. Overflow Weir in Action.' Shadow of steel knife edge which forms the lip of the weir can be seen through the falling sewage. in which x and y are the coordinates. The origin is in the upper surface of the stream vertically above the end of the invert of the pipe. The ordinate y is measured vertically downwards. V is the velocity of approach in feet per second. These expressions are applicable to any diameter of sewer up to 10 or 15 feet. They should not be used for depths of flow greater than about 14 inches; nor for slopes of more than 25 per 1,000; nor for velocities less than 1 foot per second nor more than 10 feet per second. The expression for the ordinate of the inside curve is not good for less JUNCTIONS 121 than 6 inches nor more than 5 feet. The expression for the ordi- nate of the outside curve is limited to values between the origin and 5 feet below it. The expression for the length of an overflow weir of the type shown in Fig. 45, necessary to discharge a given quantity, is in the form, in which I =the length of the weir in feet; V =the velocity of approach in feet per second; d =the diameter of the pipe in feet; hi = the head of water on the upper end of the weir; ti2 = the head of water on the lower end of the weir. In the design of an overflow weir by this formula the height of the weir above the invert of the sewer and the flow over the weir should be determined arbitrarily. The height should be sub- tracted from the computed depth of water above the weir to determine the value of hi. The difference between the flow over the weir and the flow above the weir will represent the rate of flow in the sewer below the weir. The value of h^ can then be computed as the difference in the depth of flow below the weir and the height of the weir above the invert. The value of V is computed from Kutter's formula. The length of the weir is determined by substituting these values in the formula. 64. Junctions. At the junction of two or more sewers the elevation of the inverts should be such that the normal flow lines are at the same elevation in all sewers. The sewers should approach the junction on a steep grade to prevent sewage backing up in one when the other is flowing full. The velocity of flow at the junction should not be decreased and turbulence should be avoided in order to prevent sedimentation and loss of head. The junction should be effected on smooth easy curves with radii at least five times the diameter of the sewer where possible. Curves with short radii cause backing up of sewage thus reducing the capacity of the sewers. The terms bellmouth or trumpet arch are sometimes applied to the junction of sewers large enough to be entered by a man. In small sewers the Y branches and special junctions are manu- factured so that the center lines of the pipes intersect, and the 122 APPURTENANCES junctions of mains and laterals are made in manholes. In the construction of a bellmouth the arch is carried over all the sewers. A manhole should be constructed at these junctions as clogging frequently occurs there, due to swirling and back eddies which cannot be avoided. 65. Outlets. The outlets to a sewerage system discharging into a swiftly running stream must be protected against wash and floating debris. In a stream or other body of water subject to wide variations in elevation the backing up of the sewage during high water should be avoided. Where tidal flats or low ground about the outlet may be alternately submerged and uncovered the discharge should always be into swiftly running water. In quiescent bodies of water such as lakes and harbors, and in rivers where the dilution is low, and in many other cases, the sewer outlet should be submerged. Outlets are protected against wash and the impact of debris by the construction of deep foundations and heavy protecting walls. Although the construction of an outlet in a slow current or a back eddy would avoid danger from wash and debris, the discharge of the sewage into the most rapid current possible aids in the prevention of a local nuisance. A row of batter piles on the upstream or exposed side of the sewer is desirable, or it may be necessary to construct a break-water to prevent the wash of the current from dislodging the pipe. These break-waters are low dams of wood or broken stone, more or less loosely thrown together. The back- ing up of water into the sewer can be prevented by constructing the sewer above PIG. 46. Tide Gate. the outlet on a steep grade. Where this is not possible the use of tide gates will be helpful. A tide gate, one form of which is shown in Fig. 46, is a special form of check valve placed on the end of the sewer. Sewer outlets are sometimes constructed on long trestles in order to rea'ch deep or running water. Such a trestle is shown in Fig. 47. In Boston the outlet sewers are submerged under the harbor and discharge through outlets well out in the tidal currents. The sewage is discharged under pressure and the pumps are OUTLETS 123 operated at some of the stations only at such times as the tidal currents will carry the sewage away from the harbor. It is not always necessary in a combined sewerage system to carry the Half Cross Section 9 9 9 9 Half Elevation. 6"fac/'ftg Portl. Concrete, /'/ Granite Powder-^ Concrete . ^** Vl * ^ 8 "Facing PorH. Concrete "***> I ' '/ Granite Po wder Longitudinal Section. FIG. 47. Sewer Outlet on a Trestle. Eng. News, Vol. 49, p. 9. storm flow to a distant submerged outlet. A double outlet can be constructed as shown in Fig. 48 in which the dry-weather flow is carried to the channel in a submerged sewer and the storm 124 APPURTENANCES J / n Extreme H.W.+3.76 El +3 1 I/' r/_/rJo flow is discharged on the bank. 1 Cast-iron pipe should be used for submerged outlets as the sewer is subject to disturbance by the currents, anchors, ice, and other causes. 66. Foundations. Sewers constructed in firm dry soil require no special foundation to dis- tribute the weight over the sup- porting medium. In soft ma- terials the lower half of the sewer ring may be spread as shown in Fig. 22, and in rock the pressures on sewer pipes are evenly distributed by a cushion of sand. In FIG. 48.-Dry Weather and Storm Wet g rOUnd Such as ^ u[ck ' Sewer Outlet at Minneapolis, Min- san d, mud, swamp land, etc., nesota. a foundation must be con- En g . Record, Vol. 63, p. 383. structed if the water cannot be drained off. The permissible intensities of pressure on foundations in various classes of material allowed by the building codes in differ- ent cities are given in Table 25. These figures are based on the assumption that the material is restrained laterally, which is generally the condition in sewer construction. In the softer materials it becomes necessary to spread the foundations not only to reduce the intensity of pressure, but also to care for the thrust of the sewer arch. The arch thrust may be found by one of the methods of arch analysis, and the haunches spread to care for this, or the sewer invert may be transversally reinforced to assist in caring for this action. Some sewer sections in hard and soft material are shown in Fig. 22 and 23. On soft foundations such as swamps or for outfalls on the muck bottom of rivers the sewer may be carried on a platform. For small sewers 2-inch planks, 2 to 4 feet longer than the diameter of the pipe are laid across the trench, and the sewer rests directly upon them. For large sewers imposing a heavy concentrated load, a pile foundation should be constructed. The foundation may consist of piles alone, pile bents, or a wooden platform sup- ported on pile bents. The load which can be carried by a pile is 1 Multiple Outlet for Calumet Intercepting Sewer, by S. T. Smetters, Eng. News-Record, Vol. 83, 1919, p. 728. FOUNDATIONS / TABLE 25 ALLOWABLE BEARING VALUE ON SOILS IN VARIOUS CITIES From Proc. Am. Soc. Civil Engrs., Vol. 46, 1920, p. 906 125 Quicksand and alluvial soil 5 to 1 ton per sq. ft. for Providence, R. I., 5 ton per sq. ft. for 6 cities Soft clay 1 ton per sq. ft. for 27 cities, - ton per sq. ft. for New Orleans, 2 to 3 tons for Providence, R. I. Moderately dry clay and fine sand, clean and dry 2 tons for 7 cities, If to 2 i for Chicago, 2J tons for Louisville, 2 to 4 tons for Providence, 3 tons for Grand Rapids and Los Angeles Clay and sand in alternate layers 2 tons for 19 cities, 1J to 2\ for Chicago, 3 to 5 tons for Providence Firm and dry loam or clay, or hard dry clay or fine, sand 3 tons for 24 cities, 2$ tons for 2 cities, 2 to 3 tons for Atlanta, 3j tons for Philadelphia, 4 tons for 6 cities Compact coarse sand, stiff gravel or natural earth 4 tons for 25 cities, 3i tons for Buffalo, 3 to 4 tons for Atlanta, 4 to 5 tons for Cincinnati, 5 tons for Denver, 4 to 6 tons for 3 cities, 6 tons for Rochester, N. Y. Coarse gravel, stratified stone and clay, or rock inferior to best brick masonry 6 tons for 3 cities, 5 tons for 2 cities, 8 tons for 1 city Gravel and sand well cemented 8 tons for 5 cities, 6 tons for 2 cities, 8 to 10 tons for 1 city Good hard pan or hard shale 10 tons for 4 cities, 6 tons for 2 cities, 8 tons for 1 city Good hard pan or hard shale unex- posed to air, frost or water 8 tons for 1 city, 10 to 15 tons for 1 city, 12 to 18 tons for 1 city Very hard native bed rock 20 tons for 5 cities, 15 tons for 1 city, 10 tons for 1 city, 25 to 50 tons for 1 city Rock under caisson 24 tons for Baltimore, 25 tons for Cleveland determined with accuracy only by driving a test pile and placing a load on it. Where piles do not penetrate to a firm stratum the load they will support can be determined by any one of the various formulas, either theoretical or empirical, which have been devised. Probably the best known of these formulas are the so-called Engineering News formulas one of which is : P = -Q TT ^ or a P^ e driven by a drop hammer, 126 APPURTENANCES in which P = the safe load on the pile in pounds. The factor of safety is 6; TF = the weight of the hammer in pounds; A = the fall of the hammer in feet; $=the penetration of the pile in inches at the last driving blow. The blow is assumed to be driven on sound wood without rebound of the hammer. Reference should be made to engineering handbooks for other forms of pile formulas. The accuracy of all of these formulas is not of a high degree. The piles are driven at about 2 to 4 feet centers, to a depth of from 8 to 20 feet, unless hard bottom is struck at a lesser depth. The butt diameter of the piles used for the smallest sewers is about 6 to 8 inches. If bents are used, 2 or 3 piles are driven in a row across the line of the sewer and are capped with a timber. For brick, block, pipe, and some concrete sewers, a wooden plat- form must be constructed between the pile bents for the support of the sewer. 67. Underdrains. The construction of special foundations can sometimes be avoided by laying drains under the sewers, thus removing the water held in the soil. The laying of the under- drains facilitates the construction of the sewer and reduces the amount of ground water entering the sewer. The underdrains usually consist of 6- or 8-inch vitrified tile laid with open joints from 1 to 2 feet below the bottom of the sewer as shown in Fig. 1. If the sewers are large, parallel lines of drains may be laid beneath them. An observation hole should be constructed from the bottom of the manhole to each underdrain. This hole usually consists of a 6- or 8-inch pipe, embedded in concrete, connected to the drain and open at the top. It is too small to permit effective cleaning of the underdrains, which are usually neglected after construction, and which as a result clog and cease to function. Since the principle period of usefulness of the drains is during construction, their stoppage after the work is completed is not serious. The hollow tile used in vitrified block sewers serve as underdrains after construction, but are of little or no assistance to the draining of the trench during construction, CHAPTER VII PUMPS AND PUMPING STATIONS 68. Need. In the design of a sewerage system it is occasion- ally necessary to concentrate the sewage of a low-lying district at some convenient point from which it must be lifted by pumps. In the construction of sewers in flat topography the grade required to cause proper velocity of sewage flow necessitates deep . excavation. It is sometimes less expensive to raise the sewage by pumping than to continue the construction of the sewers with deep excavation. In the operation of a sewage-treatment plant a certain amount of head is necessary. If the sewage is delivered to the plant at a depth too great to make possible the utilization of gravity for the required head, pumps must be installed to lift the sewage. In the construction of large office buildings, business blocks, etc., the sub-basements are frequently constructed below the sewer level. The sewage and other drainage from the low portion of the building must therefore be removed by pumping. Because pumps are often an essenti.il part of a sewerage system, their details should be understood by the engineer who must write the specifications under which they are purchased and installed. 69. Reliability. If the only outlet from a sewerage system is through a pumping station, the inability of the pumps to handle all of the sewage delivered to them may so back up the sewage as to flood streets and basements, endangering lives and health and destroying property. Such an occurrence should be guarded against by providing sufficient pumping capacity and machinery of the greatest reliability. 70. Equipment. The equipment of a sewage pumping station, in addition to pumping machinery, may include a grit chamber, a screen, and a receiving well. The grit chamber and screen are necessaiy to protect the pumps from wear and clogging. Grit chambers are not necessary in sewage devoid of gritty matter, 127 128 PUMPS AND PUMPING STATIONS such as the average domestic sewage, unless reciprocating pumps are used. Sufficient gritty matter is found in average domestic sewage to have an undesirable effect on reciprocating pumps. Receiving wells are used in small pumping stations where the capacity of the pumps is greater than the average rate of sewage flow. The pumps are then operated intermittently, the pumps standing idle during the time that the receiving well is filling. Except for a few types of pumps of which the valve openings are unsuitable, any machine capable of pumping water is capable of pumping sewage which has been properly screened. The principles of sewage pumps are then similar to principles of water pumps. The conditions under which these principles are applied differ but slightly in the character of the liquid, and a smaller range of discharge pressures. Pumps with large passages, dis- charging under low heads are more commonly found among sewage pumps. 71. The Building. The pumping station should, if possible, be of pleasing design and should be surrounded by attractive grounds. The Calumet Sewage Pumping Station in Chicago is shown in Fig. 49. Its architecture is pleasing particularly in FIG. 49. Calumet Sewage Pumping Station, Chicago, Illinois. contrast with its location and immediate surroundings. Such structures tend to remove the popular prejudice from sewerage and to arouse interest in sewerage questions. Service to the CAPACITY OF PUMPS 129 public is of value. It can be rendered more easily by arousing public interest and co-operation by the erection of attractive structures, than by feeding popular prejudice by the construction of miserable eyesores. 72. Capacity of Pumps. The capacity of the pumping equip- ment should be sufficient to care for the maximum quantity of sewage delivered to it, with the largest pumping unit shut down, and the provision of such additional capacity as, in the opinion of the designer, will provide the necessary factor of safety. Pumps can usually be operated under more or less overload. Power pumps and centrifugal pumps driven by constant speed electric motors have no overload capacity. A power pump or a centrifugal pump may be overloaded up to the maximum horse- power of any variable speed motor or steam engine driving it, provided the pump has been designed to permit it. Direct-acting steam pumps which are designed for proper piston speed and valve action at normal loads, can carry a 50 per cent overload for short periods, although the strain on the pump is great. They will carry a 20 to 25 per cent overload for about eight hours with less vibration and strain. The use of pumps capable of working at an appreciable overload is somewhat of an additional factor "of safety, but the overload factor should not be taken into considera- tion in determining the capacity of the pumping equipment. The load on a pumping station consists of the quantity of sewage to be pumped and the height it must be lifted. Variations in the quantity are discussed in Chapter III. The head against which the pumps must operate fluctuates with the level in the tributary sewer or pump well, and in the discharge conduit. For a free discharge or discharge into a short force main the greater the rate of sewage flow the smaller the lift, as the depth of flow in the tributary sewer increases more rapidly than that in the discharge conduit. If the discharge is into a large body of water or under other conditions where the discharge head is approxi- mately constant, the fluctuations in total head should not exceed the diameter of the tributary sewer. Such fluctuations are of minor importance in the operation of direct-acting steam pumps, but may be of great importance in the operation of centrifugal pumps, as is brought out in Art. 78. 73. Capacity of Receiving Well. The use of receiving wells is restricted to small installations which require, in addition to 130 PUMPS AND PUMPING STATIONS the standby unit, only one pump, the capacity of which is equal to the maximum rate of sewage flow. When the receiving well has been pumped dry the pump stops, allowing the well to fill again. Although the use of a large receiving well, or an equaliz- ing reservoir, for a large pumping station would permit the opera- tion of the pumps under more economical conditions, the storage of sewage for the length of time required would not be feasible. The sewage would probably become septic, creating odors and corroding the pumps. The extra cost of the reservoir might not compensate for the saving in the capacity and operation of the pumps. The capacity of the receiving well should be so designed that the pump when operating will be working at its maximum capacity, and the period of rest during conditions of average rate of flow should be in the neighborhood of 15 to 20 minutes. For example, assume an average rate of flow of 2 cubic feet per second, with a maximum rate of double this amount. The pump should have a capacity of 4 cubic feet per second, and if the receiving well is to be filled in 15 minutes by the average rate of sewage flow its capac- ity should be 15X5X60X7.5 or 14,000 gallons. Under these circumstances the pump will operate 15 minutes and rest 15 minutes, during average conditions of flow. 74. Types of Pumping Machinery. The two principal types of pumping machines for lifting sewage are centrifugal pumps and reciprocating pumps. A centrifugal pump is, in general, any pump which raises a liquid by the centrifugal force created by a wheel, called the impeller, revolving in a tight casing, as shown in Fig. 50. A reciprocating pump is one in which there is a periodic reversal of motion of the parts of the pump. Centrifugal pumps are sometimes classified as volute pumps and turbine pumps. A volute pump is a centrifugal pump with a spiral casing into which the water is discharged from the impeller with the same velocity at all points around the circumference, as shown in Fig. 51. A turbine pump is a centrifugal pump in which the water is discharged from the impeller through guide passages into a collecting chamber, in such a manner as to prevent loss of energy in changing from kinetic head to pressure head. A tur- bine pump is shown in section in Fig. 51. Centrifugal pumps are sometimes classified as single stage and multi-stage. A centrif- ugal pump from which the water is discharged at the pressure TYPES OF PUMPING MACHINERY 131 created by a single impeller is called a single-stage pump. If the water in the pump is discharged from one impeller into the suction of another impeller the pump is known as a multi-stage pump. FIG. 50. Section through de Laval Single-Stage, Double-Suction Centrifugal Pump. 375 Lubricating ring. 554 380 Oil hole cap. 555 383 Oil drain tube. 555-1 404 Shaft sleeve lock nut. 556 440 Driving coupling. 560 441 Driven coupling. 563 443 Coupling check nut. 567 R 450 Coupling bolt. 451 Coupling bolt nut. 567L 452 Coupling rubber. 453 Coupling rubber steel tube. 583 500 Pump case. 567 \ 550 Bearing bracket cap. 583 / 551 Bearing. 600 552 Shaft. 692 553 Shaft sleeve, right hand thread 815 PW Impeller. 815-1 Shaft sleeve, left hand thread. Shaft stop collar, inner. Shaft stop collar, outer. Guide ring. Packing gland. Bearing. Impeller protecting ring, right hand thread. Impeller protecting ring, left hand thread. Pump case protecting ring. Labyrinth packing. Pump case cover. Impeller key. Bearing bracket, outer. Bearing bracket, inner. The number of impellers operating at different pressures deter- mines the number of stages of the pump. A three-stage pump is shown in Fig. 52. 132 PUMPS AND PUMPING STATIONS Reciprocating pumps are generally driven by steam and are either direct-acting, or of the crank-and-fly-wheel type. Power pumps are reciprocating machines which may be driven by any form of motor, to which they are connected by belt, chain or shaft. A Deming triplex power pump is shown in Fig. 53. Power --Impeller -^Diffusion Vanes Pump. Turbine Pump, Circular Case. FIG. 51. Types of Centrifugal Pumps. Volute pumps can be used only where the character of the sewage will not clog the valves nor corrode the pump. A direct-acting steam pump is one in which the steam and water cylinders are in the same straight line and the steam is used at full boiler pressure throughout the full length of the stroke. The crank-and-fly- FIG. 52. Section of a Multi-Stage Centrifugal Pump. Courtesy DeLaval Steam Turbine Co. wheel type of pumping engine permits the use of steam expan- sively during a part of the stroke, the energy stored in the fly- wheel carrying the machine through the remainder of the stroke. Reciprocating pumps are sometimes classified as plunger pumps and piston pumps. In the action of a plunger pump the water is expelled from the water cylinder, by the action of a plunger TYPES OF PUMPING MACHINERY 133 which only partly fills the water cylinder, as shown in Figs. 54 and 55. In a piston pump the water is expelled from the water cylinder by the action of a piston which completely fills the water cylinder, as shown in Fig. 63, which illustrates a direct- acting piston pump. Plungers are better than pistons for pumping sewage as the wear between the pis- tons and the inside face of the cylinder soon reduces the efficiency of the pump. Out- side packed plungers are better than the inside packed type because the packing can FlG 53. Triplex Power Pump. be taken Up without Stopping Courtesy, The Deming Co. the pump and the leakage from the pump is visible at all times. Outside packed pumps are more expensive in first cost, but are easier to maintain and have a longer life than piston pumps. In selecting a pump to perform certain work the size of the water cylinder and the speed of the travel of the piston should be investigated to insure proper capacity. The average linear travel of the piston for slow speed pumps is estimated at about 100 feet per minute, dependent on the length of stroke and the valve area. For short strokes and small valve areas the speed may be as low as 40 feet per min- ute, and for long stroke fire pumps with large valves FIG. 54. Water End of Inside Center- Packed Plunger Pump. the piston can be operated at a speed of 200 feet per minute. 1 Vertical, triple-expansion, crank-and-fly-wheel, outside- packed plunger pumps with flap valves can be operated at speeds of 200 feet per minute when lifting sewage, and when equipped 1 " Direct Acting Steam Pumps," by F. R. Nickel, 1915. 134 PUMPS AND PUMPING STATIONS with mechanically operated valves and lifting water they can be run at speeds of 400 to 500 feet per minute. The speed of travel multiplied by the volume of piston or plunger displacement, with proper allowance for slippage, will give the capacity of the pump. The slippage allowance may be from 3 to 8 per cent for the best pumps, and for pumps in poor conditions it may be a high as 30 to 40 per cent. Channel Way to Air Pump Inlet from Main Suction Pipe FIG. 55 Water End of Outside Center-Packed Plunger Pump. Courtesy Allis-Chalmers Co. There are two types of ejector pumps used for lifting sewage. One of these depends on the vacuum created by the velocity of a stream of water or steam passing through a small nozzle. The operation of this pump is described in Art. 139 and it is illustrated in Fig. 97. The other type of ejector pump is known as the com- pressed-air ejector. It is operated by means of compressed air which is turned into a receptacle containing sewage. The details of this type are explained in Art. 83 and are illustrated in Fig. 68. SIZES AND DESCRIPTION OF PUMPS 135 75. Sizes and Description of Pumps. The size of a centrif- ugal pump is expressed as the diameter of the discharge pipe in inches. It has nothing to do with the head for which the pump is suited. On the assumption of a velocity of flow of 10 feet per second through the discharge pipe the capacity of the pump can be approximated. The size of a reciprocating pump involves the expression of the diameters of the steam cylinders, the water cylinder, and the length of the stroke in inches, in the order named, beginning with the steam cylinder with the highest pressure. A complete descrip- tion of a steam pumping engine might be; 'compound, duplex, horizontal, condensing, crank-and-fly-wheel, outside-center- packed, 12"X24"X18"X24" pump. The word compound means that there are a high-pressure and a low-pressure steam cylinder; the word duplex means that there are two of each of these cylinders; the word horizontal means that the axes of these cylinders are in a horizontal plane; the word condensing means that the steam is discharged from the low-pressure cylinders into a condenser; the name crank-and-fly-wheel is self-explanatory; the name outside-center-packed means that the water cylinder is divided into two portions between which the plunger is exposed to the atmosphere, and that the packing rings are on the outside of the two portions of the cylinder as shown in Fig. 55 ; the figures shown mean that the high-pressure steam cylinder is 12 inches in diameter, the low-pressure 24 inches in diameter, the water cylin- der is 18 inches in diameter, and the stroke of the pump is 24 inches. 76. Definitions of Duty and Efficiency. The duty of a pump is the number of foot pounds of work done by the pump per million B.T.U., per thousand pounds of steam, or per hundred pounds of coal, consumed in performing the work. These units are only approximately equal as 100 pounds of coal or 1,000 pounds of steam do not always contain the same number of B.T.U. and may only approximately equal 1,000,000 B.T.U. Since 1,000,000 B.T.U. are equal to 778,000,000 foot-pounds of work, a pump with a duty of 778,000,000 will have an effi- ciency of 100 per cent. The efficiency of a pump is therefore its duty based on B.T.U. divided by 778,000,000. The efficiencies or duties of various types of pumps are given in Table 26. 1 1 From Heat Engines, by Allen and Bursley. 136 PUMPS AND PUMPING STATIONS TABLE 26 APPROXIMATE DUTIES OF STEAM PUMPS Small duplex, non-condensing 10,000,000 Large duplex, non -condensing 25,000,000 Small simple, flywheel, condensing 50,000,000 Large simple, flywheel, condensing 65,000,000 Small compound, flywheel, condensing 65,000,000 Large compound, flywheel, condensing 120,000,000 Small triple, flywheel, condensing 150,000,000 Large triple, flywheel, condensing 165,000,000 77. Details of Centrifugal Pumps. A section of a centrifugal pump with the names of the parts marked thereon is shown in Fig. 50. Among the important parts which require the attention of the purchaser are: the impeller (PW), the impeller packing rings (567 R & L), the bearings (551, 563), the thrust bearings (555-1), the shaft (552), and the shaft coupling (440). The impeller should be of bronze, gun metal, or other alloy, because there is no rusting or roughening of the surface, and the efficiency does not fall with age. Normal fresh sewage is not corrosive, but septic sewage and sludge are usually so corrosive that iron parts cannot be used with success in contact with them. The impeller should be machined and polished to reduce the fric- tion with the liquid. Impellers are made either closed or open, i.e., either with or without plates on the sides connecting the blades to avoid the friction of the liquid against the side of 'the casing. The closed type of impeller is shown in Fig. 50. Closed impellers are slightly more expensive, but generally give better service and higher efficiencies than the open type. Single impeller pumps should have an inlet on each side of the impeller to aid in balancing the machine, unless the plane of the impeller is to be horizontal when operating. Multi-impeller pumps usually have single inlet openings for each impeller. Vibration in the pump is sometimes caused by an unbalanced impeller. The moving parts may be balanced at one speed and unbalanced at another. To determine if the moving parts are balanced the pump should be run free at different speeds and the amount of vibration observed. If the impeller is removed from the pump its balance when at rest can be studied by resting it on horizontal knife edges. If there is a tendency to rotate in any direction from any position the impeller is not perfectly balanced. DETAILS OF CENTRIFUGAL PUMPS 137 Packing rings are used to prevent the escape of water from the discharge chamber back into the suction chamber. These rings should be made of the same material as the impeller. Labyrinth type rings, as shown in Fig. 50, are sometimes used as the long tortuous passages are efficient in preventing leakage. The bearings must be carefully made because of the high speed of the pump. They are usually made of cast iron with babbitt lining. They should be placed on the ends of the shaft on the outside of the pump casing, as shown in Fig. 50, and should be split horizontally so as to be easily renewed. Exterior bearings are oil lubricated by means of ring or chain oilers with deep oil wells. Where interior bearings are necessary, because of the length of the shaft, they should be made of hard brass and should be water lubricated. Thrust bearings or thrust balancing devices are used to take up the end thrust which occurs in even the best designed pumps. To overcome this pumps are designed with double suction, opposed impellers, or two pumps with their impellers opposed may be placed on the same shaft. Due to inequalities in wear, workmanship or other conditions, end thrust will occur and must be cared for. Various types of thrust bearings are in successful use, such as: the piston, ball, roller or marine types. The marine type thrust bearing is shown in Fig. 56. The piston type of FIG. 56. Marine Type Thrust Bearing. Courtesy, DeLaval Steam Turbine Co. hydraulic balancing device is shown in Fig. 57. In the figure A represents the impeller, and B a piston fixed to the shaft and revolving with it. There is a passage for water through the open- ings (1), (2), and (3) leading from the impeller chamber to the atmosphere or to the suction of the pump. If the impeller tends to move to the right opening (1) is closed resulting in pressure on 138 PUMPS AND PUMPING STATIONS the right of the impeller forcing it to the left. If the impeller moves to the left (1) is opened thus transmitting pressure to 'the piston B forcing the impeller to the right. The flange C is not essential, but is advantageous in pumps handling gritty matter. As the channel (2) wears larger the pressure against the piston decreases allowing it to move to the left. This partially closes (3) building up the pressure again. Flexible shaft couplings should be used if the shaft of the driving motor and the pump are in the same line, as direct align- ment is difficult to obtain or to maintain. Where connected to steam turbines, reduction gearing and rigid couplings are usually used on sewage G pumps to obtain slow speed and per- 'i 2''H~ mit large passages. Flexible coup- FIG. 57. Piston Type of Thrust lingsare of various types, oneof which Balancing Device. is shown in Fig. 50. A rigid coup- ling would be formed by bolting the flanges firmly together. Shaft couplings are usually not necessary where the pump is driven by belt connection to the engine or motor, or where the pump and pulley rest on only two bearings. The stuffing box shown in Fig. 50 is packed loosely with two layers of hemp between which is a lantern gland, in order to permit a small amount of leakage. A drip box is placed below this gland to catch the leakage and return it to the pump. The leakage is permitted as it aids in lubrication and the tightening of the gland will cause binding of the shaft. The gland on the suction side of the pump should be connected by a small pipe to the discharge chamber in order to keep a constant supply of water for lubrica- tion and to prevent the entrance of air to the suction end of the pump. 78. Centrifugal Pump Characteristics. The capacity of a centrifugal pump is fixed by the size and type of its impeller and by the speed of revolution. Roughly, the capacity of a pump, for maximum efficiency, varies directly as the speed of revolution, the discharge pressure varies as the square of the speed, and the power varies as the cube of the speed. These' relations are found not to hold exactly in tests because of internal hydraulic friction in the pump. CENTRIFUGAL PUMP CHARACTERISTICS 139 The characteristic curves for a centrifugal pump, or the so- called pump characteristics, are represented graphically by the relation between quantity and efficiency, quantity and power necessary to drive, and quantity and head, all at the same speed. The quantities are plotted as abscissas in every case. The curve whose ordinates are head and whose abscissas are quantities is known as " the characteristic." The curve showing the relation between quantities and speeds is sometimes included among the characteristics. Characteristics of pumps with different styles of impellers are shown in Fig. 58. Fig. 59 shows the character- istics of a pump run at different speeds, the efficiencies at these Type L 10 20 30 40 50 60 70 80 Capacity in Gallons per Minute FIG. 58. Characteristics of Centrifugal Pumps with Different Styles of Impellers at Constant Speed. speeds when pumping at different rates, and the maximum effi- ciency at different speeds. It is to be noted that the informa- tion given in this figure is more extensive than that in Fig. 58. The operating conditions under any head, rate of discharge, and speed are given. The curves of constant speed are parallel, and their distances apart vary as the square of the speed. The line of maximum efficiency is approximately a parabola. A study of the characteristics of any particular pump should be made with a view to its selection for the load and conditions under which it is to be used. Among the important things to be con- sidered in the selection of a centrifugal pump for the expected conditions of load are: the capacity required, the maximum and minimum total head to be pumped against, the maximum varia- tions in suction and discharge heads, and the nature of the drive. For example, the pump, whose characteristics are shown in Fig. 140 PUMPS AND PUMPING STATIONS 59, should be operated at about 800 revolutions per minute. Under total heads between 40 and 50 feet, the discharge for the 100 200 500 400 500 .600 700 800 900 1000 1100 1200 1300 Capacity in Gallons per^Minute FIG. 59. Efficiency and Characteristic Curves of a Centrifugal Pump at Different Speeds. best efficiency will vary between 600 and 670 gallons per minute. The efficiencies of centrifugal pumps increase with their capacities as is shown approximately in Fig. 60. 79. Setting of Centrifugal Pumps. In setting a centrifugal pump, care should be taken to provide a firm foundation to hold the shafts of the pump and the electric motor or the reduction gearing in good alignment, 20 Size of Pumps in Inches 30 40 so or to prevent the pump from being FIG. 60. Efficiencies of Cen- trifugal Pumps. displaced by the pull of a belt. It is desirable that the foundation be level. Centrifugal pumps should be set sub- merged for small pumping stations automatically controlled. Sludge pumps must be set submerged as otherwise they will not prime successfully. Provision should be SETTING OF CENTRIFUGAL PUMPS 141 made by which the pump can be lifted from the sewage, or sludge, for inspection and repair. In many cases the pump can be made self -priming by setting it in a dry. water-tight vault below the low level of sewage flow. Where possible it is desirable not to set the pump submerged as it will receive better care when easily acces- sible. The suction pipe should be free from vertical bends where air might collect and should be straight for at least 18 to 24 inches from the pump casing. An elbow on the suction pipe, attached directly to the casing of the pump gives a lower efficiency than a suction pipe with a short straight run. Centrifugal pumps will operate with as high a suction lift as reciprocating pumps, but at the start they must be primed and some provision must be made for priming them. The suction pipe should be equipped with foot valves to hold the priming, or some method may be provided for exhausting the air from the suction pipe. The foot valves should be so installed as to form no appreciable obstruction to the flow of water. They should have an area of opening at least 50 per cent greater than the cross-section of the suction pipe. A strainer on the suction pipe is un- desirable as it becomes clogged and is usually in an inaccessible position for cleaning. A screen should be placed at the en- trance to the suction well to prevent the entrance of objects that are likely to clog the pump. A gate-valve and a check-valve should be provided on the dis- charge pipe, the former to assist in controlling the rate of dis- charge and the latter to prevent back flow into the pump when it is not operating. Centrifugal pumps are well FlG 61. -Centrifugal Pump in Man- adapted to service in either large hole at Duluth, Minn, or small units. An installation En g . Contracting, vol. 43, 1915, P . 310. in a manhole at Park Point, Duluth, is shown in Fig. 61. This station is controlled by an automatic electric device which is operated by a float in the suc- Ventilator 24"M.H. Cover. Float- 142 PUMPS AND PUMPING STATIONS tion pit. Such automatic control is an added advantage of the use of electrically driven centrifugal pumps. The Calumet Pumping Station in Chicago, shown in Fig. 49, has a capacity of approximately 1,000 cubic feet per second. The simplicity of the layout of this station is shown in Fig. 62. FIG. 62. Interior Arrangement of the Calumet Sewage Pumping Station, Chicago. Eng. News-Record, Vol. 85, 1920, p. 872. 80. Steam Pumps and Pumping Engines. The direct-acting steam pump, one type of which is shown in Fig. 63, is adapted to pumping sewage the character of which will not corrode or clog the valves. In this form of pump it is necessary to utilize the steam at full pressure throughout the entire length of the stroke, which results in high steam consumption. A fly-wheel permits the use of steam expansively during a part of the stroke, thus increasing the economy of operation. Other devices used for the same purpose are known as compensators. They are not in general use. Steam engines are classified in many different ways, for example ; according to the type of valve gear, as, plain slide valve, Corliss, Lentz, etc.; or according to the number of steam expan- STEAM PUMPS AND PUMPING ENGINES 143 sions, as, simple, compound, triple expansion, etc.; or according to the efficiency of the machine as low duty or high duty; or as 152 FIG. 63. Section of Duplex -Piston Steam Pump. Courtesy, The John H. McGowan Co. STEAM END 2 Steam cylinder and housing combined. 8 Steam piston head. 9 Steam piston follower. 10 Steam piston inside ring. 11 Steam piston outside ring (2). 12 Steam cylinder head. 14 Steam chest. 16 Steam chest cover. 17 Steam slide valve. 18 Steam valve rod. 20 Steam valve rod, pin and nut. 22 Steam valve rod, collar and set screw. 23 Steam valve rod, stuffing box. 24 Steam valve rod, stuffing box, nut and gland. 38 Piston rod. 47 Piston rod stuffing box. 48 Piston rod, stuffing box, nut and gland. 49 Valve gear stand. 51 Long valve crank and shaft. 52 Short valve crank and shaft. PUMP END 115 Pump body. 127 Brass liner. 129 Water piston head. 130 Water piston follower. 137 Cylinder head. 139 Valve plate. 140 Cap 152 Suction flange. 161 Discharge flange. 162 Valve seat, suction or discharge. 163 Valve, suction or discharge. 164 Suction valve spring. 167 Discharge valve spring. 168 Valve plate, suction or discharge. 169 Valve stem, suction or discharge. STEAM END 55 Crank pin. 56 Valve rod link. 61 Long rocker arm. 62 Short rocker arm. 63 Rocker arm wiper. 69 Cross head. condensing or non-condensing, etc. Throttling engines or auto- matic engines refer to the method of control of the steam by the governor. In throttling engines the governor controls the amount 144 PUMPS AND PUMPING STATIONS of opening of the throttle valve, in automatic engines the governor controls the position of the cut-off. The simple slide-valve, low-duty, non-condensing, throttling engine, is the lowest in first cost and the most expensive in the consumption of fuel. The triple-expansion Corliss, or the non- releasing Corliss, high-duty pumping engine is the most expensive in first cost but consumes less steam for the power delivered than any other form of reciprocating engine. For pumps of very small capacity the cost of fuel is not so important an item as the first cost of the machine. For this reason and because of the lower 9x8 Non Condensing, Jhrottlinq ' 'iqh Speed, Single Valve 125 K. W. Non Condensing, Aufomah'c, High Speed Single Valve 75 K. W. Condensing, ffofary 4 Valve, MediumSpeei 125 K.W. Compound Condensing, Automatic, HighSpeed,SmgleValve- 400 K.W. Compound" Condensing, Medium Speed, Popperr Valve 40 60 80 Per Cent of Rated Load I.I ll| Condensing, Medium Speed, Rotary 4 Valve Compound Condensing, Medium Speed, Poppetr Valve 600 &00 Horse Power FIG. 64. Diagram Showing Rates of Steam Consumption for Different Size Units under Different Loads. cost of attendance low-duty pumps are more frequently found in small pumping stations. The steam consumption per indicated horse-power, better known as the water rate of the engine, for various types of engines at full and at part load is shown in Fig. 64. The steam consump- tion of other types at full load is shown in Table 27. The indi- cated horse-power (I.H.P.) of a steam engine is the product of the mean effective pressure (M.E.P.), the area of the steam STEAM PUMPS AND PUMPING ENGINES 145 TABLE 27 WATER RATES OF PRIME MOVERS AT FULL AND PART LOADS Power, I >er Cei it of F ull Loa i Boiler Type of Engine K.W. 25 50 75 100 125 Press, Lbs. Single cylinder, high speed, non-condensing 25 250 33 42 27 37.5 26.3 35 27.0 34.0 27.5 34.0 100 to 150 Automatic, flat four valve, high speed 150 250 32 33 30 31 26.5 28 29.0 30.0 100 to 125 Tandem compound condensing, high speed 125 23 25 19 20 17 19.5 18 21 100 to 150 Cross compound, condensing, high speed 30 26 24 23 23.5 125 Cross compound, non-condensing, highspeed 39 31 27 26 27.5 125 Single cylinder Corliss, condensing 120 500 23.7 26.3 20.4 22.8 19 21.3 18.5 20.8 19.0 21.3 100 125 Compound Corliss, condensing 16.5 14 12.5 12.1 12.5 100 22.2 19 17.0 16.5 17.0 150 Single cylinder, rotary four valve, non-con- densing 75 400 26.2 35.0 22.3 27.2 21.3 26.4 21.6 26.0 22.8 26.8 100 180 Rotary four valve, tandem compound non- condensing 125 600 32.0 40.0 22.0 28.3 20 23.2 18.25 22.5 18.5 22.7 100 150 Cross compound, non-condensing rotary four valve 125 600 25 39.4 21 28 19.1 22.3 18.5 20.6 19.0 20.7 100 150 Single cylinder, poppett valve, non-con- densing 120 600 22.7 28.5 20.5 26.0 19.7 25.0 19.1 24.3 20.1 25.5 100 150 Single cylinder, poppett valve, condensing 120 600 18.5 24.6 16.7 22.3 16.1 21.4 15.6 20.8 16.4 21.9 100 150 Compound condensing, poppett valve 200 1200 14.2 18.4 13.0 16.9 12.5 16.3 12.2 15.9 12.9 16.8 100 150 Uniflow 125 600 14.6 15.0 13.7 14.3 13.4 13.7 13.4 13.5 13.3 14.0 150 . Steam turbines, condensing, Allis-Chalmers 300 2000 24 31.9 17 26.3 160 23.8 16.5 23.0 125 175 Steam turbines, condensing, Westinghouse 300 2000 13.7 18.2 12.8 16.9 12.2 16.2 12.6 16.8 125 175 Steam turbines, high pressure, non-con., 12" to 36" wheel, 1000 to 3600 R.P.M. 4 to 8 stages 28.5 116.5 Ditto. Condensing, 26-inch 17 3 112.0 146 PUMPS AND PUMPING STATIONS pistons, the length of the stroke, and the number of strokes per unit of time. A common form of this expression is, 33,000' in which P = the M.E.P. in pounds per square inch; L = the length of the stroke in inches; A = the sum of the areas of the pistons in square inches; AT = the number of revolutions per minute. The I.H.P. multiplied by the mechanical efficiency of the machine will give the brake or water horse-power, that is, the horse-power delivered by the machine. The product of the M.E.P., the sum of the areas of the steam pistons and the mechanical efficiency of the machine, should equal the product of the total head of water pumped against expressed in pounds per square inch and the sum of the areas of the water pistons or plungers. The M.E.P. is determined from indicator cards taken from the steam cylinders during operation. These cards show the steam pressure on the head and crank ends of each cylinder at all points during the stroke. 81. Steam Turbines. Among the advantages in the use of steam turbines as compared with reciprocating steam engines for driving centrifugal pumps are their simplicity of operation, the small floor space needed, their freedom from vibration requiring a relatively light foundation, and their ability to operate success- fully and economically either condensing or non-condensing under varying steam pressure. They can be operated with steam at atmospheric or low pressure, thus taking the exhaust from other engines. The greatest economy of operation for the tur- bine alone will be obtained by operating with high pressure, super- heated steam and with a vacuum of 28 inches. In large units the economy of operation of steam turbines is equal to that of the best type of reciprocating engines. In order to develop the high- est economy turbines are operated at speeds from about 3,600 to 10,000 r.p.m. or greater, the smaller turbines operating at the higher speeds. As these speeds are usually too great for the operation of centrifugal pumps for lifting sewage, reduction gears must be introduced between the turbine and the pump. Although the best form of spiral-cut reduction gears may obtain efficiencies of 95 to 98 per cent, or even higher, their use, particularly in small STEAM PUMPS AND PUMPING ENGINES 147 units, is an undesirable feature of the steam turbine for driving pumps. The steam consumption of DeLaval turbines of different powers, and the steam consumption of a 450 horse-power DeLaval turbine at different loads are shown in Fig. 64. Some steam con- sumptions of other turbines are recorded in Table 27. It is to be noted that the steam consumption of the 450 horse-power turbine at part loads is not markedly greater than that at full loads. This is an advantage of steam turbines as compared with recipro- cating engines. The steam consumption of any turbine is depend- ent on the conditions of operation and is lower the higher the vacuum into which the exhaust takes place. There are two types of turbines in general use, the single stage or impulse machines, and the compound or reaction type. The DeLaval is a well-known make of the single stage or impulse type. The principle of its operation is indicated in Fig. 65, which is the trade mark of the DeLaval Steam Turbine Co. The energy of the steam is transmitted to the wheel due to the high velocity of the steam impinging against the vanes. In the compound or re- action type of machine the steam expands from one stage to the next imparting its energy to the wheel by virtue of its expansion in the passages of the turbine. For this reason the single-stage or impulse type is operated at higher speeds than the compound or reaction machines. 82. Steam Boilers. Among the important points to be con- sidered in the selection of a steam boiler for a sewage pumping station are: the necessary power; the quality of the feed water; the available floor space; the steam pressure to be carried; and the quality and character of the fuel. Tubular boilers of the type shown in Fig. 66, are lower in first cost than other types of boilers. They are not ordinarily built in units larger than 250 to 300 horse-power and where more power is desired a number of FIG. 65. The DeLaval Trade Mark, Illustrating the Principle of the DeLaval Steam Turbine. Courtesy, DeLaval Steam Turbine Co. 148 PUMPS AND PUMPING STATIONS FIG, 66. Horizontal Fire-tube Boiler. units must be used. They are objectionable because of the relatively large floor space required, and because of their relatively poor economy of operation. The efficiencies of water-tube boilers of dif- ferent types are given in Table 28. Large power units of the water-tube type, as shown in Fig. 67, although more expensive in first cost, require less floor space. Al- most any desired steam pressure can be obtained from either type but water- tube boilers are more com- monly used for high pres- sures. The grate or stoker can be arranged to burn almost any kind of fuel under either water-tube or fire-tube boilers. The use of poor quality of water in water-tube boilers is un- desirable as the tubes are more likely to become clogged than the larger passages of the fire-tube boilers. If nec- essary, a feed-water puri- fication plant should be installed, as it is usually cheaper to take the inpurities out of the water than to take the scale out of the boiler. Not less than two boiler units should be used in any power station, regardless of the demands for power, and if the feed water is bad, three or even four units should be provided, as two units may be down at any time. FIG. 67. Babcock and Wilcox Water- tube Boiler. An appreciable factor of safety is provided by the ability of a boiler to be operated at 30 to 50 per STEAM BOILERS 149 cent overload, if sufficient draft is available, but with resulting reduction in the economy of operation. The number of units provided should be such that the maximum load on the pumping station can be carried with at least one in every 6 units or less, out of service for repairs or other cause. TABLE 28 EFFICIENCIES OF STEAM BOILERS From Marks' Mechanical Engineer's Handbook Per Evap. Com- Cent B.T.U. from and bined Sq. Ft. of per at 212 Effi- Type " Furnace Grate Rated Lb. per ciency power Area Capac- Dry Lb. of Boiler ity Coal Dry and D'vTd Coal Furnace Babcock & Wilcox 300 Hand-fired 84 118.7 11,912 8.81 71.8 Babcock & Wilcox 640 Hand-fired 118 121.5 14,602 10.83 72.0 Stirling 1128 B. & W. chain grate . 187 198.3 12,130 9.51 76.1 Rust 335 Hand-fired 68 210.5 13,202 9.42 68.9 Heine 400 Green chain grate. . . 83.5 123.8 11,608 8.79 73.5 Maximum efficient y recor ied 83 The steam delivered by a boiler is the basis of the measurement of its capacity or power. A boiler horse-power is the delivery of 33,320 B.T.U. per hour. It is approximately equal to the raising of 30 pounds of water per hour from a temperature of 100 Fahrenheit, to steam at a pressure of 70 pounds per square inch, or to 34 pounds of water per hour changed to steam from and at 212 Fahrenheit, at atmospheric pressure. The horse-power of a boiler is sometimes approximated by the area of its grate or heat- ing surface. Such a method of measuring has a low degree of accuracy on account of the variations in the quality of the fuel, and the rate of combustion. For example, the rate of combustion under a locomotive boiler is high and there is less than iVth of a square foot of grate area and about 4.5 square feet of heating surface per boiler horse-power. The Scotch Marine type of boiler used on steam ships, has slightly more grate area and slightly less heating surface than the locomotive type of boiler, because the rate of combustion is lower. Stationary water-tube boilers may have 2 to 3 times as much grate area and heating surface per 150 PUMPS AND PUMPING STATIONS horse-power as is found in locomotive boilers. If a poor type of fuel is to be used the area of the grate should be increased about inversely as the heat content of the fuel. The approximate heat content of various types of fuels is shown in Table 29. TABLE 29 APPROXIMATE HEAT VALUE OF FUELS Fuel B.T.U. per Pound Pounds of Water Evaporated from and at 212 F. All heat utilized Anthracite 13,500 14.0 Semi-bituminous, Pennsylvania 15,000 15.5 Semi-bituminous best, West Virginia . . 15,000 15.8 Bituminous, best, Pennsylvania 14,450 15.0 Bituminous, poor, Illinois Lignite best Utah 10,500 11,000 10.9 11.4 Lignite poor Oregon . 8,500 8.8 ^Vood best oak 9,300 9.6 Wood poor ash 8,500 8.8 83. Air Ejectors. The Ansonia compressed-air sewage ejector is shown in Fig. 68. In its operation, sewage enters the reservoir through the inlet pipe at the right, the air displaced being expelled slowly through the air valve marked B. The rising sewage lifts the float which actuates the balanced piston valve in the pipe above the reservoir when the reservoir fills. The lifting of the valve admits compressed air to the reservoir. The air pressure closes valve A and the inlet valve at the right, and ejects the sewage through the discharge pipe at the left. As the float drops with the descending sewage it shuts off the air supply and opens the air exhaust through the small pipe at the top center. Sewage is prevented from flowing back into the reservoir by the check valve in the discharge pipe. Other ejectors operating on a similar principle are the Ellis, the Pacific, the Priestmann and the Shone. 84. Electric Motors. The most common form of alternating current electric motor used for driving sewage pumps where con- tinuous operation and steady loads are met is the squirrel-cage polyphase induction motor. These motors operate at a nearly ELECTRIC MOTORS 151 constant speed which should be selected to develop the maximum efficiency of the pump and motor set. While Fig. 59 shows the best efficiency under varying heads to be obtained with variable speed, the advantages of cost, attention, and availability make the use of a constant speed motor common. 1 This type of motor is undesirable where stopping and starting are frequent because it has a relatively small starting torque and it requires a large FIG. 68. Ansonia Compressed-Air Sewage Ejector. starting current. Such motors can be constructed in small sizes for high starting torques by increasing the resistance of the rotor, but at the expense of the efficiency of operation. Alternating current motors are more generally used than direct- current motors because of the greater economy of transmission of alternating current, but where direct current is available constant speed shunt wound motors should be adopted. 1 " The Economy Resulting from the Use of Variable Speed Induction Motors for Driving Centrifugal Pumps " by M. L. Enger and W. J. Putnam. Journal Am. Water Works Ass'n., 1920, Vol. 7, p. 536. 152 PUMPS AND PUMPING STATIONS In the selection of a motor to drive a centrifugal pump it is important that the motor have not only the requisite power, but that its speed will develop the maximum efficiency from the pump and motor combined. If the pump and motor operate on the same shaft the speed of the two machines must be the same. If the two are belt connected, the size of the pulleys may be selected so as to give the required speed. If the motor is to be connected to a power pump an adequate automatic pressure relief valve should be provided on the discharge pipe from the pump, to pre- vent the overloading of the motor or bursting of the pump in case of a sudden stoppage in the pipe. The motor must be selected to suit the conditions of voltage, cycle, and phase on the line. Trans- formers are available to step the voltage up or down to practically any value. Rotary converters are used to change direct to alter- nating current or vice versa. 85. Internal Combustion Engines. Internal combustion engines are used for driving pumps. Units are available in size from fractions of 1 horse-power to 2,000 horse-power or more, although the use of the larger sizes is exceptional. These engines are not commonly used for sewage pumping but when used they are ordinarily belt connected to a centrifugal pump, or to an electric generator which in turn drives electric motors which operate centrifugal pumps. This type of engine is more com- monly adapted to small loads, although not entirely confined to this field, as they serve admirably as emergency units to supple- ment an electrically equipped pumping station. The fuel effi- ciency of internal combustion engines is higher than for steam engines as is indicated in Table 30, but the fuel is more expensive. The four-cycle gas engine shown in Fig. 69 is the type most commonly used. Its horse-power is the product of: the mean effective pressure, the length of the stroke, the area of the piston, and the number of explosions per second divided by 550. The M.E.P. is dependent on the character of the fuel used and the compression of the gas before ignition. Producer gas will furnish mean effective pressures between 60 and 70 pounds per square inch, natural gas and gasoline, 85 to 90 pounds per square inch, and alcohol from 95 to 110 pounds per square inch. The Diesel Engine is the most efficient of internal combustion engines. The original aim of the inventor, Dr. Rudolph Diesel, was to avoid the explosive effect of the ordinary internal com- INTERNAL COMBUSTION ENGINES 153 TABLE 30 COMPARATIVE FUEL COSTS FOR PRIME MOVERS Type of Engine Quantity of Fuel per H.P. Hour Cost of Fuel in Cents per Horse-power Hour Reciprocating steam engines, simple, non- condensing 25 to 200 H P 21 to 8 Ib coal 4 2 to 16 Triple condensing, 2000 to 10,000 H.P. . 2. 3 to 1.91b. coal 0.46 to 0.37 Steam turbines, high pressure, non-con- densing, 200 to 500 K W 6 5 to 4 2 Ib coal 13 to 86 500 to 3000 K.W 2.6 to 1.91b. coal 0.52 to 0.37 Condensing 5000 to 20,000 K.W 1.8tol.431b. coal 0.36 to 0.28 Gas engines Natural gas, 50 to 200 H.P 19 to 11 cu. ft. Producer gas, 50 to 200 H P 2 to 1 5 eu ft Illuminating gas, 10 to 75 H.P 26 to 19 cu. ft. 2.1to 1.5 Gasoline, 10 to 75 H P 1 5 to 8 pints 5 6to 3 Oil engines, 100 to 500 H.P I.lto0.751b.oil NOTE. Coal assumed at $4.00 per ton, illuminating gas at 80 cents per thousand cubic feet, and gasoline at 30 cents per gallon. FIG. 69. Bessemer Oil Engim Twin Cylinder, Valve Side. 154 PUMPS AND PUMPING STATIONS bustion engine by injecting a fuel into air so highly compressed that its heat would ignite the fuel, causing slow combustion of the fuel thus utilizing its energy to a greater extent. The fuel and air were to be so proportioned as to require no cooling. Although the ideal condition has not been attained, the heat efficiency of Diesel engines is high. They will consume from 0.3 to 0.5 of a pound of oil (containing 18,000 B.T.U. per pound) per brake horse-power hour, giving an effective heat efficiency of 25 to 30 per cent. Although not now in extensive use in the United States it is probable that this engine will be more generally adopted for conditions suitable for internal combustion engines. 86. Selection of Pumping Machinery. Centrifugal pumps are particularly adapted to the lifting of sewage because of their large passages, and their lack of valves. The low lifts, nearly constant head, and the possibility of equalizing the load by means of reservoirs are particularly suited to efficient operation of centrifugal pumps. They require less floor space than recipro- cating pumps of the same capacity, and because of their freedom from vibration they do not demand so heavy a foundation. The discharge from the pump is continuous thus relieving the piping from vibration. In case of emergency the discharge valve can be shut off without shutting down the pump, an important point in " fool proof " operation. Volute pumps are better adapted to pumping sewage as their passages are more free and they are better suited to the low lifts met. Gritty and solid matter will cause wear on the diffusion vanes of turbine pumps in spite of the most careful design. Although turbine pumps can possibly be built with higher effi- ciency than volute pumps, their efficiency at part load falls rapidly and the fluctuations of sewage flow are sufficient to affect the economy of operation. Turbine pumps are more expensive and heavier than volute pumps on account of the increased size neces- sitated by the diffusion vanes. Multi-stage pumps are used for high lifts and are seldom if ever required in sewage pumping. As ordinarily manufactured, each stage is good for an additional 40 to 100 pounds pressure, but wide variations in the limiting pressures between stages are to be found. Reciprocating plunger pumps are sometimes used for sewage pumping where the character of the sewage is such that the SELECTION OF PUMPING MACHINERY 155 valves will not be clogged nor parts of the pump corroded. These pumps are seldom used in small installations or for low lifts. They are not adapted to automatic or long distance control as are electrically driven centrifugal pumps. The use of recipro- cating pumps for sewage pumping is practically restricted to very large pumping stations with capacities in the neighborhood of 50,000,000 gallons per day or more. Steam-driven pumps are the most common of the reciprocating type, but power pumps are sometimes used in special cases for small installations and may be driven by either a steam or gas engine or an electric motor. Compressed air ejectors, as described in Art. 83 are used for lifting sewage and other drainage from the basement of buildings below the sewer level. Centrifugal pumps electrically driven are, as a rule, the most satisfactory for sewage pumping. Electric drive lends itself to control by automatic devices, which are particularly convenient in small pumping stations. The control can be arranged so that the pump is operated only at full load and high efficiency, and when not operating no power is being consumed, as is not the case with a steam pump where steam pressure must be maintained at all times. The electric driven pump is thrown into operation by a float controlled switch which is closed when the reservoir fills, and opens when the pump has emptied the reservoir. The choice between steam and electric power for large pumping stations is a matter of relative reliability and economy. The selection of the proper type of pump, whether recipro- cating or otherwise, requires some experience in the consideration of the factors involved. Fig. 70 is of some assistance. In dis- cussing this figure, Chester states: " Fig. 70 attempts to represent graphically, the writer's ideas under general conditions, of the machines that should be selected for certain capacities for both principal engine and alternate and the station duty they may be expected to produce, but you must realize that this intends the principal engine doing at least 90 per cent of the work and that the head, the cost of coal, the load factor, the cost of real estate . . . the boiler pressure, and the space avail- able, and finally . . . the funds available, are factors which may shift both the horizontal and curved lines. In the field of low service pumps of 10,000,000 capacity or over, the centrifugal pump reigns supreme, and for constant 156 PUMPS AND PUMPING STATIONS low heads of 20,000,000 capacity or over the turbine driven centrifugal usurps the field." A reciprocating pump of any type would have to be specially built for pumping sewage not carefully screened or otherwise treated, as the valves, ordinarily used in such pumps for lifting water, would clog. The vertical triple-expansion pumping engine with special valves and for large installations, and the centrifugal pump for large or small installations are the only suit- Qirecf-Acting Triple Expansion,/ I 2 3 456 7 8 9 10 II \l 13 14 15 16 17 18 19 20 Capacity in Millions of Gallons per Day. FIG. 70. Expectancy Curves for Pumping Engines Working against a Pres- sure of 100 Pounds per Square Inch. J. N. Chester, Journal Am, Water Works Ass'n, Vol. 3, 1916, p. 493. able types for pumping sewage. With steam turbine or electric drive the centrifugal has the field to itself. 87. Costs of Pumping Machinery. The cost of pumping machinery can not be stated accurately as the many factors involved vary with the fluctuations in the prices of raw materials, transportation, labor, etc. The actual purchase price of machinery can be found accurately only from the seller. The costs given in this chapter are useful principally for comparative purposes and for exercise in the making of estimates. The costs of complete pumping stations are shown in Table 3 1. 1 These figures repre- sent costs in 1911.. 1 C. A. Hague in Trans. Am. Society of Civil Engineers, Vol. 74, 1911, p. 20. COST COMPARISONS OF DIFFERENT DESIGNS 157 TABLE 31 COSTS OF COMPLETE PUMPING STATIONS These costs include the best type of triple expansion engines, high-pressure boilers, brick or inexpensive stone building with slate roof, chimney and intake. Cost of land is not included. it E_i L M II M L 03 * si ft.2 fcl CO ft! L fe c PH So ^.3 |T3 SO ^^ FO -o - ft So 3*"L3 g,|| -a SI 1- III -ft Si I'Ja a|| &k ij "S 3 o* *l3 S +} t r^j O g CT rft V^ ^ -*-^ o 4-^^ c --i O* wj^ 3 +f o -^*5 2 5o02 *" <5 pL< ^K ^ o ^ Pu 00 PH 0^ QQ ^02 O ^ ^ /, ___ { **^- Q a o b K Q K o c3 30 12 562 6,750 70 28 277 7,750 110 44 200 8,750 40 16 438 7,000 80 32 250 8,000 120 48 187 9,000 50 20 362 7,250 90 36 229 8,250 130 52 192 10,000 60 24 312 7,500 100 40 213 8,500 88. Cost Comparisons of Different Designs. In the design of a pumping station and its equipment the relative costs of different designs should be compared, and the least expensive design selected, due consideration being given to serviceability, reliability, and other factors without definite financial value. In comparing the costs of different types of machinery, all items in connection with the pumping station should be considered. For example, the cost of an electrically driven centrifugal pump and equipment may be less than the total cost of a steam driven reciprocating pump and equipment because of the saving in the cost of boilers, boiler house, etc., but a comparison of the capitalized cost of the two might show in favor of the reciprocating steam pump because of the lower cost of operation. The total cost of a plant, or any portion thereof, may be considered as made up of three parts : (1) The first cost, (2) opera- tion and maintenance and, (3) renewal. The total cost S can be expressed as in which C = the first cost; = the annual expenditure for operation and mainte- nance; # = the amount set aside to cover renewal; r = the rate of interest. 158 PUMPS AND PUMPING STATIONS S is called the capitalized cost of a plant. The annual payment necessary to perpetuate a plant is The value of R is useful when expressed in terms of the life of the plant or machine and the current rate of interest. It is sometimes called the depreciation factor or capitalized depreciation. If it is borne in mind that R is the amount to be set aside at compound interest for the life of the plant, at the end of which time the accrued interest should be sufficient to renew the plant, it is evi- dent that R(l+R) n -R = C C *=(!+,.)._! in which n is the period of usefulness, or life of the plant, expressed in years, no allowance being made for scrap value. A comparison of the annual expense of three different plants is shown in Table 32. It is evident from this comparison that the machinery with the least first cost is not always the least expen- sive when all items are considered. A sinking fund is a sum of money to which additions are made annually for the purpose of renewing a plant at the expiration of its period of usefulness. The annual payment into the sinking fund is equivalent to the term Rr in the expression for annual cost, or in terms of C, r, and n, the annual payment is Cr It is the same as the capitalized depreciation multiplied by the rate of interest. The expression ,.. , \ n _i * s sometimes called the rate of depreciation. The present worth of a machine is the difference between its first cost and the present value of the sinking fund. If m repre- sents the present age of a plant in years, then the present worth is p=c(i- Where straight-line depreciation is spoken of it is assumed that the worth of a machine depreciates an equal part of its first cost COST COMPARISONS OF DIFFERENT DESIGNS 159 h EH 02 tj * SiO M 00 Q O O 00 -t O5 O O IQ 5 PI 1 -2-53" (N ill l-sl o >o c^i o |l .S fe *** cc ^ """::: S3 S 1-8 I 3 : o 10 o . U5 rt rl B "SSr ;:::: : || : : : : 49 a .5 V : -g : : : : Cl 2 S : "3 * i j O 1 *. -e -2 a c ; 1 3 ; : : . : S . ^ .5 TJ g a O _J 05 c 6 r= ^ 13 a o3 0> 3 O c3 3 4> ^ pu ^ pq 3 fe pj 3 160 PUMPS AND PUMPING STATIONS each year. For example, if the life of a plant is assumed to be 20 years, straight-line depreciation will assume that the plant loses 2^ f its original value annually. The present worth of a plant under this assumption would be the product of its first cost and the ratio between its remaining life and its total life. This method of estimating depreciation and worth is frequently used, particularly for short-lived plants and for simplicity in book- keeping, but it is less logical than the method given above. 89. Number and Capacity of Pumping Units. In order to select the number and capacity of pumping units for the best economy, a comparison of the costs of different combinations of units should be made and the most economical combination determined by trial. The principles outlined in the preceding articles should be observed in making these comparisons. In a steam pumping station, when the number of units operating is less than the average daily maximum for the period, steam must nevertheless be kept on a sufficient number of boilers to operate the maximum number of pumps. This, and corresponding standby losses must not be overlooked, as they may show that a smaller number of larger units is ultimately more economical. TABLE 33 SUMMARY OF FLUCTUATIONS OF SEWAGE FLOW AT A PROPOSED PUMPING STATION R* 8 1 R* 8 a R*8 -c g Q o g -tj h O 5 Si gg S3 p|g | h *so !^ 1 1 *o O fl Q) 1 *oO 00 1 > fc-3 d o"i a u M S fl o"S . PR * S-2 ^ 8, .Silo I3.S *ll I ' a 1 J3S P 1 3 E 3 m i 1 l 293 6.0 450 45 51 13.4 173 12 29 15.0 111 8 163 8.6 354 41 50 13.5 169 8 24 15.6 95 15 119 10.0 300 30 45 13.8 158 5 20 16.0 79 18 106 10.6 284 28 44 13.9 154 3 16 16.5 65 23 88 11.2 249 23 40 14.2 143 2 14 16.8 58 31 69 12.2 211 21 38 14.4 137 1 6.5 18.0 29 32 65 12.4 204 18 35 14.6 129 Total horse-power days for one year, 102,000. Average load in horse-power, 280. For example, the sewage flow expected at a proposed pumping station is shown in Table 33. The steps involved in the selection NUMBER AND CAPACITY OF PUMPING UNITS 161 Is Is g orse-p Type I If asaq; patJIBQ SI ' spanod OOO'OT s^tufi spunoj 'lO^-^cococcJjT-iCNiNCNeN! OC-COCOOO^HlOrH^li-IC^l-l I-H O5 Tt< O <-H O "- 1 X O O2 CO TjH i-l (> (N O "* (N O X N ( I CD 00 * I-H CN -CO OOOOIN :o ^^^: SS ::::::; CM t^ t>- US 10 GO iO O I-H 00 O) O CM 5O GO ^ i-l -CO "CiMOOOOO -O S :::::: :| :: :g aaAvod-asjojj uipvoi o^occw . , 1 -5 4J jn H 'd'H uiBaig spunod . . . .^-ioO -O5CO >.t -oos -o -os^-i ^U 1 ', ', ', ',',',', ', ', CO 162 PUMPS AND PUMPING STATIONS CO HH a a lO IO O H ft OOQ r-t T i O ^ (M TtH ilSllllli rrH rH oTr- Tt^ 1 |> c^ CO O^ ^> nc invert riclc *' >nc. sides \ . 166 " roof ) minting up, etc.*. 1 167 Balance on hand to-night 87 Smpty cement bags on hand 1 Full bags used to-day ast night 7 167 Pmntv Viacr^ ^r*nt in fn1av Total 164 .. ' 140 Empty bags balance on hand to-night- 24-... Materials received. From. J 47- imounts. -4x6 16 _/*_// -ft.... ,. ..12- -ft.; E" " N". . 1120' t* roofers -116 ft. -} 19-tt. -t30-tt. Steel Bars. Car No.PRR 7284 190- 120- 76- Sheeting and bracing left in None Forcnicin* FIG. 87. Foreman's Daily Material Report. From Engineering and Contracting, 1907. report on materials. The total cost must be made up in the office from these records and a knowledge of unit costs. Equipment consists of tools, animals, machinery, and appara- tus used in construction. Only equipment that is actually used should be charged to the job and a credit should be made at the completion of the job for the fair value of the equipment remain- ing after the completion of the work. Overhead charges include the expense of the office force, superintendence, and miscellaneous items such as insurance, rent, 238 CONSTRUCTION transportation, etc., which cannot be charged to any particular portion of the work but are equally applicable to all portions. It happens frequently that many jobs are handled in the same main office. The division of overhead becomes more difficult and is frequently arranged on an arbitrary basis, e.g., each job may be charged the proportion of overhead that its contract price bears to the total contract prices being performed under that office. This rule may be modified when it becomes evident that some job is taking distinctly more than its share of the overhead. Estimates of work done in any period can be made with the above data in hand by subtracting the total costs of the work up to the beginning of the period from the total costs up to the end of the period. Fig. 88 shows a sample blank from the final esti- mate sheets used at Scarsdale, N. Y. 124. Progress Reports. 1 These are kept by the engineer in order that he may see that the work is progressing as called for in the contract, and any portion which is lagging behind without reason may be pushed. Such reports are most useful when the information is expressed graphically, as the eye quickly catches points where the work is falling behind schedule. 125. Records. The contract drawings are supposed to show exactly where and how construction is to be done. Due to unexpected contingencies changes occur, of which a record should be made and preserved. These records may be kept in a form similar to the contract drawings, or if the changes are not exten- sive, they can be recorded on the original contract drawings. The location of house and other connections should be recorded in a separate note book available for immediate consultation. The engineer should keep a diary of the work in which are recorded events of ordinary routine as well as those of special interest and importance. This diary should be illustrated by photographs showing the condition of the streets before and after construction, methods of construction, accidents, etc. Such accounts are of great value in defending subsequent litigation and their existence sometimes prevents litigation. A contractor may wait a year or so after the completion of a piece of work until the engineer and other city officials have broken their connection with the city. Suit is then brought against the city and unless good records are 1 See Planning and Progress on a Big Construction Job, by Chas Penrose, Eng. News-Record, Vol. 84, 1920, pp. 554 and 627. COST DATA AND ESTIMATES 239 24-" VIT. SEWER .6 FT. TO 8 FT. DEEP, INCLUDING & FT. 1914 LOCATION SCHEDULE FEET PRICE AMOUNT tfj^\7\&vctnMH*+&M.H*S (&*t&4.'&<) "This siqn indioates that the item has been inch A tded in t 2GO.O f 203 ft 406. U* he monthly estimate V-BRANCHES ON 24" PIPE LOCATION SCHEDULE NUMBER PRICE AMOUNT fra.7*2p552*5 <***4 A 6 4*c : 24. 00* gr 1914 |S MANHOLES 6FTTO8FT LOCATION SCHEDULE PRICE AMOUNT M, 5 ^^^^^^ A SD.OO . J~0. CO* 1914 o MANHOLE DEPTHS EXCEEDING 6 FT. LOCATION SCHEDULE FEET PRICE AMOUNT ?/ [&eto^^*^4|*$^* K 4-. 3 p.fffff /2. 10* 191.4 ROCK IN SEWER TRENCH LOCATION SCHEDULE CO.YDS PRICE AMOUNT 4* 2^PfF^2~25 ^' " J 4-1 ZfS L //4. // | 1914 fe QC . R 'C K IN MANHOLE EXCAVATION LOCATION SCHEDULE CU. YDS. PRICE AMOUNT *4* ^^^^^^^B, F /4 * t '. Of Z.15^ o JO. ** o < Rj*l .EN6TH55^2 CONTINGENT EXTRAS STAN DARD-A-SECTION CONCRETE FOR SEWERS LOCATION . SCHEDULE CU. YDS. PRICE AMOUNT Z73.8 24 3 "A 1914 CONTINGENT EXTRAS EDULE BOARD Ff. PRICE AMOUNT //* o. 31. ?Q FIG. 88. Samples of Cost Record Forms. From Engineering and Contracting, 1909. 240 CONSTRUCTION available the administration may be forced to buy the claimant off or may elect to enter court, only to be beaten. EXCAVATION 126. Specifications. The following abstracts have been taken from the specifications on Excavation by the Baltimore Sewerage Commission as illustrative of good practice. In conducting the work the contractor shall: . . . remove all paving, or grub and clear the surface over the trench, whenever it may be necessary and shall remove all surface materials of whatever nature or kind. He shall properly classify the materials removed, separat- ing them as required by the Engineer; and shall properly store, guard, and preserve such as may be required for future use in backfilling, surfacing, repaving or otherwise. All macadam material removed shall be separated and graded into such sizes as the Engineer may direct and materials of different sizes shall be kept separate from each other and from any and all other materials. All the curb, gutter, and flag-stones and all paving material which may be removed, together with all rock, earth and sand taken from the trenches shall be stored in such parts of the carriageway or such other suitable place, and in such manner as the Engineer may approve. The Contractor shall be responsible for the loss of or damage to curb, gutter and flag-stones and to paving material because of careless removal or wasteful storage, disposal, or use of the same. . . . When so directed by the Engineer the bottom of the trench shall be excavated to the exact form of the lower half of the sewer or of the foundation under the sewer. The bottom width of the trench for a brick or concrete sewer shall be ... not less in any case than the overall width of the sewer, as shown on the plans. In case the trench is sheeted this minimum width will be measured between the interior faces of the sheeting as driven, but in no case shall bracing, stringers, or waling strips be left within any portion of the masonry of the sewer except by permission of the Engineer; and such braces, stringers and waling strips shall not, in any case, be allowed to remain within the neat lines of the masonry as shown on the plans. In case that the distance between faces of the sheeting is less than that called for by the width of the SPECIFICATIONS 241 sewer to be laid in the trench, the Engineer may direct the sheeting to be drawn and redriven, or otherwise changed and altered; or he may direct that the sewer be reinforced in such manner and to such an extent as he may deem necessary without compensation to the Contractor, even though such narrower trench was not caused by negli- gence or other fault on the part of the Contractor. Trenches for vitrified pipe shall be at all points at least six inches wider in the clear on each side than the greatest external width of the sewer, measured over the hubs of the pipe . . . Bell holes shall be excavated in the bottoms of trenches for vitrified pipe sewers wherever necessary. Not more than three hundred feet of trench shall be opened at any one time or place in advance of the com- pleted building of the sewer, unless by written permission of the Engineer and for a distance therein specified. . . . The excavation of the trench shall be fully completed at least twenty feet in advance of the construction of the invert, unless otherwise ordered. During the progress of construction the Contractor will be required to preserve from obstruction all fire hydrants and the carriageway on each side of the line of the work. The streets, cross walks, and sidewalks shall be kept clean, clear, and free for the passage of carts, wagons, car- riages and street or steam railway cars, or pedestrians, unless otherwise authorized by special permission in writ- ing from the Engineer. In all cases a straight and con- tinuous passageway on the sidewalks and over the cross walks of not less than three feet in width shall be pre- served free from all obstruction. Where any cross walk is cut by the trench it shall be temporarily replaced by a timber bridge at least three feet wide, with side railings, at the Contractor's expense. The placing of planks across the trench without proper means of connection or fastenings, or pipe or other material, or the using of any other makeshift in place of properly con- structed bridges, will not be permitted. This is equally applicable to certain wagon bridges to be fixed upon by the Engineer, on the basis of traffic requirements. In streets that are important thoroughfares or in narrow streets the material excavated from the first one hundred feet of any opening or from such additional length as may be required, shall upon the order of the Engineer, be removed by the Contractor, as soon as excavated. The material subsequently excavated shall be used to refill the trench where the sewer has been built. 242 CONSTRUCTION The preceding specifications are applicable to open-trench excavation. Rigid restrictions are placed about tunneling because of the greater difficulty of doing good work, the greater danger to life and property and the possibility of later surface subsidence if the backfilling is done improperly. A common clause in specifications is: All excavations for sewers and their appurtenances shall be made in open trenches unless written permission to excavate in tunnel shall be given by the Engineer. 127. Hand Excavation. Earth excavation by pick and shovel is the simplest and most primitive mode of excavation. Only small jobs are handled in this manner in order to save the invest- ment necessary in machines or the expense of hiring and moving one to the work. The tools used in the hand excavation of trenches are:' picks, pickaxes, long-handled and short-handled pointed shovels, square-edged long- and short-handled shovels, scoop shovels, axes, crowbars, rock drills, mauls, sledges, etc. The excavating gangs are divided up into units of 20 to 50 men under one foreman or straw boss, and among the men may be a few higher priced laborers who set the pace for the others. Each laborer on excavation should be provided with a shovel, the style being dependent on the character of the material being excavated and the depth of the trench. In stiff material and deep trenches requiring the lifting of the material in the shovel, long-handled pointed shovels should be used. In loose sandy material loaded directly into buckets short-handled, square pointed shovels are satisfactory. Picks are used in cemented gravels or where hard obstructions prevent cutting down with the edge of the shovel. Very stiff but not hard material can be cut out in chunks with a pickaxe and thrown from the trench or into a bucket with a scoop shovel. Scoop shovels are also useful in wet running quicksand. The number of picks, axes, crowbars, and other tools must be proportioned according to the material being excavated. Under the worst conditions of excavation in a hard cemented gravel it may be necessary to provide each man with a pick as well as a shovel, whereas in sand only a shovel is necessary. Two or three crowbars, axes, a length of chain, two or .three screw jacks, etc., are provided per gang in case of an unexpected encounter with an obstruction in the trench, such as a boulder, a tree stump, a length of pipe, etc. HAND EXCAVATION 243 In laying out the work the foreman marks the outlines of the trench on the ground by means of a scratch made with a pick, chalk marks, tape, or other devices. These marks are measured from offset or center stakes set by the engineer. Center stakes are less conducive to error but are more likely to be disturbed before use than are offset stakes, but careless foremen make more errors with offset than with center stakes. The inspector should assist or be present at the laying out of the trench. After the trench has been laid out each laborer should be given a certain specific portion of it to dig and this portion is marked out on the ground. In this way a check can be kept upon the performance of each laborer and the knowledge of this fact tends to a uni- formly better performance. The amount of work that can be performed by one man with a pick and shovel is as shown in Table 49. Some men may exceed these rates, many will not attain them. The allotted task must be gaged on the character of the ground in order that the tasks may be equal and a spirit of competition fostered. The hard worker will set the pace for the lazy man. Some contractors have adopted the expedient of dis- missing laborers for the day as soon as the allotted task is done. TABLE 49 AMOUNT OF MATERIAL MOVED BY ONE MAN WITH A PICK AND SHOVEL (From H. P. Gillette) Material Cubic Yard per Hour Material Cubic Yard per Hour Hardpan 0.33 Sand 1.25 Common earth O.Sto 1.2 Sandy soil 8 to 1 2 Stiff clay Clay 0.85 1 00 Clayey earth Sandy soil (frozen) 1.3 75 The opening of the trench may be facilitated by breaking ground with a plow. In hard ground or on paved roads it may be necessary to cut through the surface crust with a hammer and drill, although in some cases a plow can be used successfully. Frozen ground can be thawed by building fires along the line of the trench, or greater economy may be achieved by placing steam pipes along the surface with perforations about every 18 inches 244 CONSTRUCTION and either boxing them on the top and sides .or burying them in the frozen earth with a covering of sand. Another arrangement is to blow steam into a line of bottomless boxes in which each box is about 8 feet long. Holes are left in the top of the boxes into which the pipe is shoved, and after its withdrawal the holes are covered. Blasting of frozen earth is sometimes successful but cannot be resorted to in built up districts where it is unsafe unless properly controlled. Once the frost crust is broken through it can be attacked from below and frequently broken down by undermining. A laborer cannot dig and raise the earth much more than to the height of his head, and preferably not quite so high, without tiring quickly. After the trench has passed a depth of 4 feet he cannot throw the earth clear of the trench. An additional laborer is needed then at the surface to throw the earth back. He should shovel the earth from a board platform placed at the edge of the trench as a protection to the bank. When the trench passes the 6-foot depth a staging is put in about 4 feet from the top on which the lowest laborer piles his materials. It is then passed up to the surface by a second laborer on the staging, and a third laborer on the surface throws the material back clear of the trench. Stag- ings are put in about every 5 or 6 feet for the full depth of the trench. When the trench has come within half the diameter of the pipe of the final grade, if the material is sufficiently firm, the remainder of the trench should be cut to conform to the shape of the lower half of the outside of the pipe, with proper enlargements for each bell. 128. Machine Excavation. On work of moderately large magnitude excavation by machine is cheaper than by pick and shovel alone. In comparing the cost of excavation by the two methods all items such as sheeting, pipe laying, backfilling, etc., should be included, since these items will be affected by the method of excavation. The cost of setting up and reshipping the machine must be included as this is frequently the item on which the use of the machine depends. Because of the cost of setting up and shipping, which must be distributed over the total number of yards excavated, the cost per cubic yard of excavating by machine varies with the number of cubic yards excavated. The point of economy in the use of a machine is reached when the cost by hand MACHINE EXCAVATION 245 and by machine are equal. For all work of greater magnitude, excavation by machine will prove cheaper. 1 Items favoring the use of machinery which may cause its adoption for small jobs are: its greater speed, reliability, ease in handling, economy in sheet- ing, economy in labor, and small amount of space needed making it useful in crowded streets. Continuous bucket machines, drag lines, and occasionally steam shovels are not adapted to conditions where rocks, pipes and other underground obstacles are frequently met. The following problem is an example of the work necessary in making a comparison of the relative economy of machine and hand excavation: It is assumed that a man can excavate 15 feet of trench 30 inches wide and 8 feet deep in 10 hours. He receives 55 cents per hour for his work. A machine costing $10,000 has a life of 6 years. It can be kept busy 150 days in the year. When operating it costs $1.25 per hour for the operator, fuel and repairs. It will excavate 800 linear feet of 30 inch trench to a depth of 8 feet in 10 hours. It is assumed that capital is worth 10 per cent on such a venture and that the sinking fund will draw 10 per cent. If the cost of moving and setting up the machine is $1,800, how many cubic yards of excavation must there be to make excavation by machine economical. Costs of sheeting, pumping, etc., are assumed to be the same for machine or hand work. Solution. For hand work the man excavated 1.11 cubic yard per hour at 55 cents. The relative cost of hand excavation is then 50 cents per cubic yard. The cost of machine work will be divided into : interest on first cost; operation and repairs; and sinking fund for renewal. The interest on the first cost of $10,000 at 10 per cent is $1,000 per year. The machine works 1,500 hours in the year. Therefore the cost per hour is $0.67. The sinking fund payment, as found from sinking fund tables or the accumulation of $10,000 in 6 years, is $1,300 per year or per hour for 1,500 hours is $0.87. The cost of operation per hour is given as $1.25. The total cost per hour is therefore $2.79. The machine excavated 59.3 cubic yards per hour which makes the cost, exclusive of moving, equal to $0.47 1 See also " Ownership and Operation of Trench Excavators by the Water Department of Baltimore," by V. B. Seims, presented before Am. Water Works Association, June 9, 1921. CONSTRUCTION per cubic yard. In order to equalize the cost of machine and hand excavation the cost of moving the machine must be divided among a sufficient number of cubic yards so that the cost per cubic yard shall be 3 cents. The cost of moving is given as $1,800. This amount divided among 60,000 cubic yards equals 3 cents per cubic yard. Therefore the job must provide at least 60,000 cubic yards of excavation in order that the use of the machine shall be justifiable from the viewpoint of economy alone. 129. Types of Machines. Machines particularly adapted to the excavation of sewer and water pipe trenches are of four types: (1) continuous bucket excavators; (2) oVerhead cable way or track excavators; (3) steam shovels; and (4) boom and bucket excava- tors. Other types of excavating machinery can be used for sewer trenches under special conditions. Machines are ordinarily limited to a minimum width of trench of 22 inches. Between widths of 22 inches and 36 inches the limit of depth for the first class of machines is about 25 feet. For other types of machines there is no definite limit, though the economical depth for open cut work seldom exceeds 40 feet. 130. Continuous Bucket Excavators. Continuous bucket excavators are of the types shown in Figs. 89 and 90. The buckets which do the digging and raising of the earth may be supported on a wheel as in Fig. 89 or on an endless chain as in Fig. 90. The support of the wheel or endless chain can be raised or lowered at the will of the operator so as to keep the trench as close to grade as can be done by hand work. In some machines the shape of the buckets can be made such as to cut the bottom of the trench, in suitable material, to the shape of the sewer invert. In operation, the buckets are at the rear of the machine and revolve so that at the lowest point in their path they are traveling forward. The excavated material is dropped on to a continuous belt which throws it on the ground clear of the trench, into dump wagons, or on to another continuous belt running parallel with the trench to the backfiller, by means of which the excavated material is thrown directly into the backfill without rehandling. The body of the machine supporting the engine travels on wheels ahead of the excavation and is kept in line by means of the pivoted front axle. When obstacles are encountered the excavating wheel or chain is raised to pass over the obstacle, and allowed to dig itself in on the other side. CONTINUOUS BUCKET EXCAVATORS 247 FIG. 89. Buckeye Wheel Excavator. Courtesy, Buckeye Traction Ditcher Co. FIG. 90. Buckeye Endless-chain Excavator. Courtesy, Buckeye Traction Ditcher Co. 248 CONSTRUCTION Wheel excavators are not adapted to the excavation of sewer trenches over 3 to 4 feet in width and 6 to 8 feet in depth. The endless-chain excavators are suitable for depths of 25 feet with widths from 22 to 72 inches, and due to the arrangement permit- ting buckets to be moved sideways they will cut trenches of differ- ent widths with the same size buckets. This is an advantage where there are to be irregularities in the width of the trench such as for manholes or changes in size of pipe. With excavating machines pipe can be laid within 3 feet of the moving buckets and the trench back- filled immediately, thus mak- ing an appreciable saving in the amount of sheet- ing. In the construction of trenches for drain tile at Garden Prairie, Illinois, the sheeting was built in the form of a box or shield, fastened to the rear of the machine and pulled along after it as is shown in Fig. 91. The performance of this type of excavating machine under suitable conditions is large. A remarkable record was made by Ryan and Co. in Chicago, 1 with an excavating machine. 1338 feet of 32-inch trench were excavated to an average depth of 8 feet in 7 hours, or an average of 160 cubic yards per hour. More could have been accomplished if it had not been for delays in supplies. Another crew at Greeley, Colorado, 2 with a Buckeye endless-chain ditcher weighing 17 tons and costing $5200, averaged 232 cubic yards per day for 300 days, and the cost was 10.7 cents per cubic yard. A 15-ton Austin excavator can be expected to remove 300 to 500 cubic yards per day. The cost of operation of the machines is made up of items listed in Table 50. The figures given are merely suggestive. In making a comparison of the cost of hand and machine FIG. 91. Movable Sheeting Fastened to Traction Ditcher. From Eng. News-Record, Vol. 82, 1919, p. 740. 1 Eng. and Contracting, Vol. 48, 1917, p. 492. 2 Earth Excavation by A. B. McDaniel. CONTINUOUS BUCKET EXCAVATORS 249 TABLE 50 COST OF OPERATING DITCHING MACHINE Per Day Total Labor : 1 Operator at $150 per month $6 00 1 Assistant Operator at $120 per month 4 00 4 Laborers at $4 . 00 per day 16.00 fcofi no Fuel: 20 Gallons of gasoline at 28 cents 5.60 5.60 Miscellaneous : Oil waste etc 1.20 Repairs and maintenance 10 00 Interest, 6 per cent on $10,000 for 150 days Depreciation, 200 working days per year and an 8 year life 4.00 11 11 26 31 Total cost per day $57 91 TABLE 51 COMPARISON OF COST OF HAND EXCAVATION AND MACHINE EXCAVATION WITH CONTINUOUS-BUCKET EXCAVATOR Hand Work Per Day, Dollars Machine Work Per Day, Dollars Foreman 4 00 Engineer 4 00 Timberman 3 00 Fireman 2 50 Helper 2.50 Coal 5 00 40 Laborers at $2 00 80 00 Team 4 00 Foreman 4 00 Pipe layer Helper . . 3.00 2 50 2 Teams backfilling 2 Helpers Interest, depreciation and repairs 8.00 4.00 10.00 Total 95 00 Total 54 50 250 CONSTRUCTION excavation the figures given in Table 51 are from " Excavating Machinery " by McDaniel, who quotes the cost of machine exca- vation from the manufacturers of the Parsons machine issued as the result of several years' experience with their excavator. In the comparison the hand crew is assumed to dig 315 linear feet of trench 28 inches wide by 12 feet deep in a day of 10 hours. This assumes that each man will excavate 7 cubic yards per day. The machine is assumed to excavate 250 feet of the same trench. The comparison indicates that an excavator will work at about 50 per cent of the cost of hand excavation, if the cost of moving the machine is not included. FIG. 92. Carson Excavating Machine on Trench Excavation in South Mil- waukee. Courtesy, Mr. C. F. Henning. 131. Cableway and Trestle Excavators. Cableway and trestle excavators are most suitable for deep trenches and crowded conditions. They should not be used for trenches much less than 8 feet in depth. They differ from the continuous-bucket excava- tors in that the actual dislodgment of the material is done by pick and shovel, the excavated material being thrown by hand into the buckets of the machine. A machine of the Carson type is shown in Fig. 92. The machine consists of a series of demountable frames held together by cross braces and struts to form a semi- rigid structure. An I beam or channel extending the length of CABLEWAY AND TRESTLE EXCAVATORS 251 the machine is hung closely below the top of the struts. The lower flange of this beam serves as a track for the carriages which carry the buckets. All the carriages are attached to each other and to an endless cable leading to a drum on the engine. This cable serves to move the buckets along the trench. The buckets are attached to another cable which is wound around another drum on the engine and serves to lower or raise all the buckets at the same time. In operation there are always at least two buckets for each carriage, one in the trench being filled and the other on the machine being dumped. There should be a surplus of buckets to replace those needing repairs. The machines may be from 200 to 350 feet in length, and the number of buckets which can be lifted at one time varies from one to a dozen or more. On trenches over 5 to 6 feet in width a double line of buckets is sometimes used. The entire machine rests on rollers and straddles the trench. It is moved along the trench by its own power, either by gearing or chains attached to the wheels, or by a cable attached to a dead-man ahead. The Potter trench machine differs from the Carson in that only 2 buckets are used at a time and these are carried on a car which travels on a track on top of the trestle. The movement of the buckets and the car are controlled by 2 dump men who ride on the car and who can raise or lower the buckets inde- pendently. The organization needed to operate these machines is: a lockman who locks and unlocks the buckets on the cable, a dumper, as many shovelers as there are buckets on the machine, and an engineman who is usually his own fireman. From 50 to 400 cubic yards of material can be excavated in a day with one of these machines, dependent on the character of the material and the depth of the trench. H. P. Gillette in his Handbook of Cost Data reports that about 190 cubic yards were excavated per day with a Potter machine. The machine was 370 feet long. Six f-yard buckets were used, 4 in the trench and 2 on the carrier. The trench was 10J feet wide and 18 feet deep in wet sand and soft blue clay. The organization consisted of an engineman, a fireman, 2 dumpmen on the carrier, and from 17 to 21 excavating laborers depending on the kind and the amount of the excavation. In general the capacity of such machines is limited by the amount of material which can be shoveled into them by hand. 252 CONSTRUCTION 132. Tower Cableways. These are essentially of the same class as the trestle cableway machines. They differ in that the carriage supporting the buckets travels on a cable suspended between 2 towers instead of on a track supported on a trestle. As a rule only one bucket is handled in the machine at a time. They are used in sewer work only in exceptional cases as the towers must be taken down and re-erected each time that there is an advance in the trench greater than the distance between the towers. 133. Steam Shovels. The use of steam shovels for the exca- vation of sewer trenches is becoming more prevalent because of their growing dependability and durability as compared with other machines, their adaptability for small trenches, and the relatively large number of widely different uses to which they can be put. In excavating a trench the shovel straddles the trench and runs on tractors, wheels, or rollers on either side of it. The shovel cuts the trench ahead of it. As a result it is difficult to set sheeting and bracing close to the end of the trench while the shovel is operating. Steam shovels are therefore not suitable for excava- tion in unstable material, unless the sheeting is driven ahead of the excavation. It is only in the softest ground that ordinary wood sheeting can be driven ahead of the excavation. Steel sheet piling is more suitable for such use. Fig. 93 1 shows a shovel at work on a trench in Evanston, Illinois. Shovels are equipped with extra long dipper handles to adapt them to trench excavation. The dipper handle in the picture is longer than the standard for this type of machine. The method of supporting the shovel can be seen in the picture under the machine and the method of bracing and of finishing the trench by hand work are also shown. The excavated material is taken out in the shovel and dropped on the bank or into wagons. The limiting depth to which trenches can be excavated by steam shovels is about 20 to 25 feet, where the trench is too nar- row for the shovel to enter. Wider trenches are cut in steps of about 15 feet, the shovel working in the trench for additional depths. Shovels are now made to cut trenches as narrow as a man can enter to lay pipe. The greatest width that can be cut from one position of the shovel is from 15 to 40 feet, dependent on the size of the shovel. Occasionally a combination of a drag line 1 Courtesy, Sanitary District of Chicago. STEAM SHOVELS 253 and a steam shovel can be used, as on the construction of the Calumet sewer in Chicago. On this work the first step was cut by a steam shovel. It was followed by a drag line resting on the step thus prepared, and excavating the remaining distance to grade. The depth of the trench in this work averaged about 25 to 30 feet. Steam shovels are rated according to their tonnage and the capacity of the dipper in cubic yards. Both are necessary as the size of the dipper is varied for the same weight of machine, dependent on the char- acter of the material being excavated. For rock the dipper is made smaller than for sand. Gillette in his Hand Book of Cost Data gives the coal and water con- sumption of steam shovels as shown in Table 52. The per- formance of ^^ FiG^^i^mShov^t Work cm Sewer Trench shovels is recorded f or North Shore Intercepting Sewer, Evanston, in Table 53. The Illinois, conditions of the work have a marked effect on the output of the shovel. A shovel in a thorough cut, i.e., in a trench just wide enough for the shovel to turn 180 degrees but too narrow to run cars or wagons along side of it, will perform less than one- half of the work that it can perform in a side cut, i.e., where the cars can be run along side the shovel which turns less than 90 degrees. 254 CONSTRUCTION TABLE 52 COAL AND WATER CONSUMPTION BY STEAM SHOVELS (From Handbook of Cost Data, by H. P. Gillette) Weight in tons 35 45 55 65 75 90 Dipper, cubic yards Coal, tons per 10 hour day U 3 1 H 11 2 U 2 3 2\ Water, gallons per 10 hour day. . 1500 2000 2500 3000 4000 4500 TABLE 53 PERFORMANCE BY STEAM SHOVELS Cost in Weight Dipper Depth Width 10-Hour Cents, in Cubic of Cut, of Cut Perform- per Authority Remarks Tons Yards Feet ance Cubic Yard 25 1 9 36 in. 85 22.6 R. T. Dana Eng. Rec., 1 69:581 25 1 8 35 in. 96 23.5 do. 2 70 2 26 16 ft. 569 6.7 do. 3 30 1 15-18 60 in. 300 A. B. McDaniel Excavat- 4 ing Machinery 15 ! 14 134 ft. 400 Eng. Cont'r, 8-25-09 5 8 36 /Very \wide 16 yd. } cars / Marion Steam Shovel Co. 6 55 296 H. P. Gillette's Cost Data 7 65 2| 280 do. Greater than 78 in. \ 700 30. 6 | G. C. D. Lenth, Eng. News-Record, 85:22 8 Remarks: 1. One runner at $5.00, one fireman at $2.31, two laborers at $1.70 each, supplies at $4.50, and interest and depreciation on 200 days per year, $4.00. Total per day, $19.21. Material, clay and gravel. 2. Average of 11 jobs with the same shovel. 3. Cost per day, one runner at $5.00, one craneman at $3.60, one fireman at $2.00, 7 roller men at $1.50 each, supplies $9.00 and interest and depreciation on $9000 at 200 days per year $8.00. Total, $38.10. 4. Hard clay. 5. Stiff clay for the basement of a building in Chicago. 6. Stripping ore. This is a maximum record. The average was about three hundred and twenty 16 cubic yard cars per day. 7. Blasted mica schist. 8. General average. DRAG LINE AND BUCKET EXCAVATORS 255 134. Drag Line and Bucket Excavators. A drag line exca- vator is shown in Fig. 94. The back of the bucket is attached to a drum on the engine by means of a cable passing over the wheel in the end of the long boom. The front of the bucket is attached by another cable directly to another drum on the engine. In operation the bucket is raised by its rear end and dropped out to the extremity of the boom. It is then dragged over the ground towards the machine, digging itself in at the same time. When filled the bucket is raised by tightening up on the two cables, swung to one side by means of the movable boom, and dumped. FIG. 94. Drag Line at Work on Trench for Drain Tile. Drag line excavators will perform as much work as steam shovels under favorable conditions. They are less expensive in first cost and operation, and are equally reliable but they are not adapted to the more difficult situations where steam shovels can be used to advantage. Drag lines are suitable only for relatively wide trenches in material requiring no bracing, and in a locality where relatively long stretches of trench can be opened at one time. The bucket excavator differs from the drag line in that the bucket can be lifted vertically only and the types of buckets used in the two types of machine are different. The bucket may be self filling of the orange-peel or clam-shell type, or a cylindrical container which must be filled by hand. A drag line can be 256 CONSTRUCTION easily converted into a boom and bucket excavator. Boom and bucket excavators are well adapted to use in deep, closely braced trenches and shafts. 135. Excavation in Quicksand. 1 A sand or other granular material in which there is sufficient upward flow of ground water to lift it, is known as quicksand. Its most important property, from the viewpoint of sewer construction, is its inability to sup- port any weight unless the sand is so confined as to prevent flow- ing of the sand, or unless the water is removed from the sand. Excavation in quicksand is troublesome and expensive and is frequently dangerous. The material will flow sluggishly as a liquid, it cannot be pumped easily, and its excavation causes the sides of the trench to fall in or the bottom to rise. The founda- tions of nearby structures may be undermined, causing collapse and serious damage. These conditions may arise even after the backfilling has been placed unless proper care has been taken. The greatest safeguard against such dangers is not only to exer- cise care in the backfilling to see that it is compactly tamped and placed, but to leave all sheeting in position after the completion of the work. The ordinary method of combating quicksand and in conduct- ing work in wet trenches is to drive water-tight sheeting 2 or 3 feet below the bottom of the trench, and to dewater the sand by pump- ing. When dry it can be excavated relatively easily. A more primitive but equally successful method is to throw straw, brick- bats, ashes, or other filling material into the trench in order to hold the excavation once made, or this may supplement the attempts at pumping, or the wet sand may be bailed out in buckets. Successful excavation in quicksand requires experience, resource- fulness, and a careful watch for unexpected developments. The well points described in Art. 142 are used for dewatering quick- sand. 136. Pumping and Drainage. Ground water is to be expected in nearly all sewer construction and provision should be made for its care. Where geological conditions are well known or where previous excavations have been made and it is known that no ground water exists it may be safe to make no provision for encountering ground water. Where ground water is to be expected 1 See article by J. R. Gow, Journal New England Waterworks Ass'n, Sept., 1920, also Public Works, Vol. 50, p. 98. TRENCH PUMP 257 the amount must remain uncertain within certain rather wide limits until actually encountered. In order to avoid the necessity for pumping, or working in wet trenches it is sometimes possible to build the sewer from the low end upwards and to drain the trench into the new sewer. The wettest trenches are the most difficult to drain in this manner as the material is usually soft and the water so laden with sediment as to threaten the clogging of the sewer. It is undesirable to run water through the pipes until the cement in the joints has set. This necessitates damming up the trench for a period which may be so long as to flood the trench or delay the progress of the work. If it is not possible to drain the t v ench through the sewer already constructed the amount of water to be pumped can be reduced by the use of tight sheeting. Pumps for dewatering trenches must be proof against injury by sand, mud, and other solids in the water. For this purpose pumps with wide passages and without valves or ^ packed joints are desirable. The types of pumps used are: simple flap valve pumps improvised on the job, diaphragm pumps, jet pumps, steam vacuum pumps, centrifugal pumps, and recipro- cating pumps. All are of the simplest of their type and little attention is paid to the economy of operation because of the temporary nature of their service. 137. Trench Pump. A simple pump which can be improvised on the job is shown in section in Fig. 95. Its capacity, is about 20 gallons per minute but its operation is backaching work. It is inexpensive, quickly put together and may be a help in an emergency. It is to be noted that the passages are large and straight, that there are no FIQ Q5 packed joints, and that the velocity of flow is so improvised small that it is not liable to clogging by picking up Trench Pump, small objects. 138. Diaphragm Pump. The type of pump shown in Fig. 96 is the most common in use for draining small quantities of water from excavations. It is known as the diaphragm pump from the large rubber diaphragm on which the operation depends. The pump is made of a short cast-iron cylinder, divided by the rubber 258 CONSTRUCTION diaphragm or disk to the center of which the handle is connected. The valve is shown at the center of the disk. As the diaphragm is lifted the valve remains closed, creating a partial vacuum in the suction pipe and at the same time discharging the water which passed j through the valve on the previous down stroke. When the valve is lowered the foot valve on the suction pipe closes, holding the water in place, and the valve in the pump opens allowing the water to flow out on top of the disk to be discharged on the next up stroke. Table 54 shows the capacities of some dia- phragm pumps as rated by the manufacturers. The smaller sizes are the more frequently used and are equipped with a 3-inch suction hose with strainer and foot valve. They are not adapted to suction lifts over 10 to 12 feet. Where greater lifts are necessary one pump may discharge into a tub in which the foot valve of a higher pump is submerged. TABLE 54 CAPACITIES OF DIAPHRAGM PUMPS FIG. 96. Diaphragm Pump. Courtesy, Edson Manufacturing Co. Diameter of Diameter of Length of Capacity per Cylinder, Suction, Stroke in Stroke, Inches Inches Inches Gallons 6 3 4 0.49 8 4 6 1.47 9* 24 0.75 12t* 3 1 25 12|* Power driven by 1 horse-power engine 0.58f * Diameter of diaphragm, t Gallons per minute JET PUMP 259 139. Jet Pump. The simplicity of the parts of the jet pump is shown in Fig. 97. It has a distinct advantage over pumps containing valves and moving parts in that there are no obstruc- tions offered to the passage of solids as well as liquids through the pump. It is not economical in the use of steam, however. It operates by means of a steam jet entering a pipe at high velocity through a nozzle. This action causes a vacuum which will lift water from 6 to 10 feet. The lower the suction lift, however, the greater the efficiency of the work. The sizes and capacities of jet pumps as manufactured by the J. H. McGowan Co. are shown in Table 55, FIG. 97. McGowan Steam Jet Pump. Courtesy, The John H. McGowan Co. TABLE 55 CAPACITIES OF JET PUMPS (J. H. McGowan Co.) Size of Pump Capacity, Approximate and Discharge Pipe, Steam Pipe, Gallons Horse-power Suction Pipe, per Required Inches Inches Inches Minute I \ 1 8 2 1 1 1 15 3 H 1 i 20 4 H u I 30 6 2 n ! 40 8 2 2 i 50 10 3 2^ i 60 15 4 3^ H 85 25 140. Steam Vacuum Pumps. This type of pump depends on the condensation of steam in a closed chamber to create a vacuum which lifts water into the chamber previously occupied by the 260 CONSTRUCTION steam and from which the water is ejected by the admission of more steam. The best known pumps of this type are the Pulsom- eter, manufactured by the Pulsometer Steam Pump Co., the Emerson, manufactured by the Emerson Pump and Valve Co.; and the Nye Pump, manufactured by the Nye Steam Pump and Machinery Co. A section of a Pulsometer is shown in Fig. 98. It consists of two bottle-shaped chambers A and B with their necks communi- K-2 Sect! Discharge FIG. 98 Pulsometer Steam Vaccum Pump. eating at the top and each opening into the outlet chamber through a check valve. Steam is admitted at the top and enters chamber A or B according to the position of the steam valve C as shown. This steam valve is a ball which is free to roll either to the right or left and forms a steam-tight joint with whichever seat it rests upon. In normal operation chamber A would be filled with water as the steam enters the cylinder. At the same time a check valve at the top opens to admit a small quantity of air which forms a cushion insulating the steam from the water, reduces the condensation of the steam, and serves as a cushion STEAM VACUUM PUMPS 261 for the incoming water on the opposite stroke. The pressure of the steam depresses the surface of the water without agitation and forces the water through the check valve F into the discharge chamber 0. When the water falls to the level of the discharge chamber the even surface is broken up and the intimate contact of the steam and water condenses the former instantaneously. This forms a vacuum in chamber A which, assisted by a slight upward pressure in chamber B caused by the incoming water, immediately pulls the ball C over to the other seat and directs the steam into chamber B. The vacuum in chamber A now draws up a new .charge of water through the suction pipe into the chamber. A section of the Emerson pump is shown in Fig. 99. The pump consists of two vertical cylinders B and C. Each chamber has a suction valve L at the bottom, opening up- ward from a common chamber from which the discharge pipe U extends. On the top of each chamber is a baffle plate G which operates to distribute the steam evenly to the two chambers and to prevent it from agitating the surface of the water in the chambers. A condenser nozzle F is con- nected with the bottom of the opposite chamber by a pipe into which a check valve opens upward. As the pressure in the chamber alternates water will be injected through F into the opposite chamber and condense the steam therein, promptly forming a vacuum. An air valve P admits a small quantity of air while the chamber is filling with water, the air acting as an insulating cushion as in the Pulsometer. Valve 0, just above the top connection S is used to regulate the amount of steam that FIG. 99. Emerson Steam Vaccum Pump. 262 CONSTRUCTION enters the pump. The top connection S has two ports, one leading to each chamber. An oscillating valve enclosed in it admits the steam through these ports to the two chambers alternately. This valve is driven by a small three-cylinder engine, the crank shaft of which extends into the top connection in the center of the bearing on which the valve oscillates. A positive geared connection is made between the valve and the engine and so arranged that the engine will run faster than the valve. The action of these pumps consists of alternately filling and emptying the two chambers. They will continue operation with- out attention or lubrication so long as the steam is turned on. In view of the simplicity of their operation and make-up, their ability to handle liquids heavily charged with solids, and their reasonable steam consumption these pumps are widely used for pumping water in construction work. They have an added advantage that no foundation or setting is required for them as they can be hung by a chain from any available support. These pumps are manufactured in sizes varying from 25 to 2500 gallons per minute at a 25-foot head, and with a steam con- sumption of about 150 pounds per horse-power hour. They reduce about 4 per cent in capacity for each 10 feet of additional lift. They will operate satisfactorily between heads of 5 to 150 feet, with a suction lift not to exceed 15 feet. Lower suction lifts are desirable and the best operation is obtained when the pump is partly submerged. The steam pressure should be balanced against the total head. It varies from 50 to 75 pounds for lifts up to 50 feet, and increases proportionally for higher lifts. The dryer the steam the lower the necessary boiler pressure. 141. Centrifugal and Reciprocating Pumps. The details of these pumps, their adaptability to various conditions, and their capacities are given in Chapter VII. The centrifugal is better adapted to trench pumping as it is not so affected by water con- taining sand and grit, but for clear water, high suction lifts and fairly permanent installations, reciprocating pumps can be used with satisfaction. 142. Well Points. In dewatering quicksand a method fre- quently attended with success is to drive a number of well points into the sand and connect them all to a single pump. Figure 100 shows a well point system used on sewer work in Indiana. The well points are 3 feet apart and are connected to a 2J-inch header ROCK EXCAVATION 263 which in turn is connected to six Nye pumps, each with a capacity of 200 gallons per minute for a lift of 50 feet. The number and size of well points and pumps to use will depend on conditions as met on the job. On a piece of work in Atlantic City 1 the equip- ment consisted of two complete outfits each comprising one hundred IJ-inch by 36-inch No. 60 well points, one hundred 6-foot lengths of rubber hose, about 600 feet of suction main, one hundred valved T connections, and a 7 X 8-inch Gould Triplex Pump with a capacity of 200 gallons per minute, belted to a 7| horse-power moto r . FIG. 100. Well Points Pumped by Nye Steam Vacuum Pump. 143. Rock Excavation. A common definition of rock used in specifications is: whenever the word Rock is used as the name of an excavated material it shall mean the ledge material removed or to be removed properly by channeling, wedging, barring, or blasting; boulders having a volume of 9 (this volume may be varied) cubic feet or more, and any excavated masonry. No soft disintegrated rock which can be removed with a pick, nor loose shale, nor previously blasted material, nor material which may have fallen into the trench will be measured or allowed as rock. Channeling consists in cutting long narrow channels in the rock to free the sides of large blocks of stone. The block is then loosened by driving in wedges or it is pried loose with bars. It is a method used more frequently in quarrying than in trench exca- . News, Vol. 75, 1916 p. 1050. 264 CONSTRUCTION vation where it is not necessary to preserve the stone intact. In blasting, a hole is drilled in the rock, and is loaded with an explosive which when fired shatters the rock and loosens it from its position. In drilling rock by hand the drill is manipulated by one man who holds it and turns it in the hole with one hand while striking it with a hammer weighing about 4 pounds held in the other hand, or one man may hold and turn the drill while one or two others strike it with heavier hammers. In churn drilling a heavy drill is raised and dropped in the hole, the force of the blow developing from the weight of the falling drill. Hand drills are steel bars of a length suitable for the depth of the hole, with the cutting edge widened and sharpened to an angle as sharp as can be used without breaking. The drill bar is usually about |th of an inch smaller than the diameter of the face of the drill. Wedges used are called plugs and feathers. They are shown in Fig. 101 which shows also the method of their use . The feathers are wedges with one round and one flat face on which the flat faces of the plug slide. 144. Power Drilling. In power drilling the drill is driven by a reciprocating machine which either strikes and turns the drill in the hole, or lifts and turns it as in churn drilling, or the drill may be driven by a rotary machine which is revolved by compressed air, steam, or electricity. There are many different types of machines suitable for drilling in the different classes of material encountered and for utilizing the various forms of power available. A. jack hammer drill is shown in Fig. 102. In its lightest form the drill weighs about 20 pounds and is capable of drilling f-inch holes to a depth of 4 feet. Heavier machines are available for drilling larger and deeper holes. The same machine can be adapted to the use of steam or compressed air. When in use the point of the drill is placed against the rock and a pressure on the FIG. 101. Plug and Feathers for Splitting Rock. POWER DRILLING 265 handle opens a valve admitting air or steam. The piston is caused to reciprocate in the cylinder, striking the head of the drill at each stroke. The drill is revolved in the hole by hand or by a mechanism in the machine. A hollow drill can be used by means of which the operator admits air or steam to the hole, thus blow- ing it out and keeping it clean. These machines have the advan- tage of small size, portability and simplicity. They can be easily and quickly set up and the drills can be changed rapidly. Their undesirable features are the vibration transmitted to the operator and the dust raised in the trench. i St'd Drill Throttle- FlG. 102. Jack Hammer Rock Drill. FIG. 103. Tripod Drill, A type of drill heavier and larger than the jack hammer drill is shown in Fig. 103. It requires some form of support such as a tripod, or in tunnel work it can be braced against the roof or sides. Some data on steam and air drills are given in Table 56. The effect of the length of the transmission pipe, temperature of the outside air, pressure at the boiler or compressor, etc., will have a marked effect on the amount of steam or air to be delivered to the drill. Compressed air is affected more than steam by these out- side factors, but it has an advantage in that as it loses in pressure it increases in volume so that the loss of power is not so marked. Gillette states: 266 CONSTRUCTION We may assume that a cubic foot of steam will do practically the same work in a drill as a cubic foot of com- pressed air at the same pressure, because neither the steam nor the air acts expansively to any great extent in a drill cylinder, due to the late cut-off. This being so ... one pound of steam is equivalent to nearly 30 cubic feet 'of free air ... all at the same pressure of 75 pounds per square inch. If a drill consumes at the rate of 100 cubic feet of free air per minute ... it would therefore consume 240 pounds of steam (at 75 pounds pressure) per hour. . . . Where not more than three or four drills are to be operated, probably no power can equal compressed air generated by gasoline. It will require 12 horse-power to compress air for each drill, hence 1J gallons of gasoline will be required per hour per drill while actually drilling. TABLE 56 DATA ON ROCK DRILLS (From H. P. Gillette) 1 Diameter of cylinder in inches 21 2^ 21 3i 31 31 Length of stroke in inches 5 6 61 6f 6f 71 Length of drill from end of crank to end of piston 36 43 50 50 50 52 Depth of hole drilled without change of bit, inches 15 20 24 24 24 24 Diameter of supply inlet. Standard pipe, inches 3 3 i 1 1 Approximate strokes per minute with 4 60 pound pressure at the drill 500 450 375 350 325 300 Depth of vertical hole each machine will drill easily, feet 6 8 10 14 16 20 Diameter of holes drilled, inches j to 1^ as desired Diameter of octagon steel, inches. . . . I to | I to 1 1 to 1| U to IJ 1| to 11 Htoll Best size of boiler to give plenty of steam at high pressure, horse-power 8 8 9 10 12 Best size of supply pipe to carry steam 100 to 200 feet, inches 1 i 3 1 1 U Weight of drill unmounted, with wrenches and fittings, not boxed, pounds . . 128 190 265 315 385 390 Weight of tripod, without weights, not boxed, pounds 80 160 160 160 210 275 Weight of holding down weights, not boxed, pounds 120 270 270 285 330 375 Cubic feet of free air per minute required to run one drill at 100 pounds 92 104 126 146 154 160 For more than one drill, multiply the value in the above line by the following factors: For 2 drills, 1.8; 5 by 4.1; 10 by 7.1; 15 by 9.5; 20 by 11.7; 30 by 15.8; 40 by 21.4; 70 by 33.2. POWER DRILLING 267 / Since gasoline air-compressors are self regulating, when the drill is not using air very little gasoline is burned by the gasoline engine driving the compressor. A gasoline com- pressor possesses other very important economic advan- tages over a small steam-driven plant. First, there is the saving in wages of firemen and second, there is the saving in hauling and pumping of water and the hauling of fuel. The cost of gasoline is often less than the cost of coal for operating a small plant. An electric drill 1 operated on the principle of the solenoid does away with motor, valves, pipes, vapor, freezing, and other difficulties attendant on the use of steam or air. The rates of drilling in different classes of rock are shown in Table 57. Frequent changes of drills and relocation of tripods will materially reduce the performance of a drill, for as much as 45 minutes may be lost in making a new set up. In this the jack hammer drills show their advantage as no time is lost in a set up. TABLE 57 RATES OF ROCK DRILLING Rates in Feet per Ten-hour Shift. Vertical Holes 10-20 Feet Deep. (From Gillette) Hard Adirondack granite 48 Maine and Massachusetts granite 45-50 Mica-schist of New York City. Possible 60-70 Mica-schist of New York City. Average 40-50 Hard, Hudson River trap rock 40 Soft red sand stone of Northern New Jersey 90 Hard limestone near Rochester, N. Y 70 Limestone of Chicago Drainage Canal 70-80 Douglass, Indiana, syenite. Difficult set ups 36 Canadian granite on Grand Trunk R. R 30 Windmill point, Ontario limestone: 3f-inch drills 75 2f-inch drills 60 2Hnch drills 37 145. Steam or Air for Power. The choice between steam or air is dependent on the conditions of the work. Steam is unde- sirable in tunnels on account of the heat produced. In open cut 1 Mun. Engineering, Vol. 53, p. 6. 268 CONSTRUCTION work it is at a disadvantage because of the loss of power due to radiation from the hose or pipe. The life of the hose is not so long as when air is used, escaping steam causes clouds of vapor which obscure the work, and serious burns may occur due to hot water thrown from the exhaust. It is advantageous since leaks may be easily discovered and remedied, it requires less machinery than air, and it is sometimes less expensive. With compressed air, gasoline or electric motors can be used for operating the com- pressors. TABLE 58 ROCK BLASTING (From Gillette) Depth Distance Distance Character of Material Powder Used per Hole of Hole, Back of Face, Hole to Hole, Feet Feet Feet Limestone of Chicago Drainage Canal 40 per cent dynamite 12 8 8 Sandstone \ 200 pounds 1 20 18 14 black powder / Granite s 2 pounds J12 41 4| to 5 60 per cent dynamite / Pit Mining, Treadwell, Mine, Alaska 12 2* 6 146. Depth of Drill Hole. The depth of the hole is dependent on the character of the work. The deepest holes can be used in open cut work where the shattered rock is to be removed by steam shovel. The face can be made 10 to 15 feet high. The depth of the hole in center cut tunnel facings are from 6 to 10 or even 12 feet. In the bench the depth is equal to the height of the bench. In narrow trenches where the rock is to be removed by derrick or thrown into a bucket by hand, the hole should be sufficiently deep to shatter the rock to a depth of at least 6 inches below the finished sewer. Frequently shooting to this depth at one shot cannot be done due to the built up condition of the neighborhood or other local factors. The depth of the hole in trench work should not much exceed the distance between holes. Deep holes SPACING OF DRILL HOLES 269 are usually desirable as a matter of economy in saving frequent set ups, but the holes cannot be made much over 20 feet in depth without increasing the friction on the drill to a prohibitive amount. 147. Diameter of Drill Hole. The diameter of the hole should be such as to take the desired size of explosive cartridge. The common sizes of dynamite cartridges are from } inch to 2 inches in diameter. In drilling, the diameter of the hole is reduced about one- eighth of an inch at a time as the drill begins to stick. This reduc- tion should be allowed for, and experience is the best guide for the size of the hole at the start. In general the softer or more faulty or seamy the rock, the more frequent the necessary reductions in size of bit. 1 For hard homogeneous rock the holes can be drilled 10 feet or more without changing the size of the drill bit. 148. Spacing of Drill Holes. The spacing of holes in open cut excavation is commonly equal to the depth of the hole. The character of the material being excavated has much to do with the spacing of the holes. The spacing, diameter and depth of holes used on some jobs is shown in Table 58. Gillette states: It is obviously impossible to lay down any hard and fast rule for drill holes. In stratified rock that is friable, and in traps that are full of natural joints and seams, it is often possible to space the holes a distance apart somewhat greater than their depth, and still break the rock to com- paratively small sizes upon blasting. In tough granite, gneiss, syenite, and in trap where joints are few and far between, the holes may have to be spaced 3 to 8 feet apart regardless of their depth for with wider spacing the blocks thrown down will be too large to handle with ordinary appliances. Since in shallow excavations the holes can seldom be much further apart than one to one and one-half times their depth we see that the cost of drilling per cubic yard increases very rapidly the shallower the excavation. Furthermore the cost of drilling a foot of hole is much increased where frequent shifting of the drill tripod is necessary. The common practice in placing drill holes is to put down holes in pairs, one hole on each side of the proposed trench; and if the trench is wide one or more holes are drilled between these two side holes 2 but in narrow trench l Yor types of drill bits see article by T. H. Proske, Mining and Scientific Press, March 5, 1910. 2 These intermediate holes are seldom more than 3 feet apart. 270 CONSTRUCTION work, such as for a 12-inch pipe, one hole in the middle of the trench will usually prove sufficient. The holes are spaced about 3 feet apart longitudinally. After the holes have been completed they should be plugged to keep out dirt and water. SHEETING AND BRACING 149. Purposes and Types. Sheeting and bracing are used in trenching to prevent caving of the banks and to prevent or retard the entrance of ground water. The different methods of placing wooden sheeting are called stay bracing, skeleton sheeting, poling boards, box sheeting, and vertical sheeting. Steel sheeting is usually driven to secure water tightness and if braced the bracing is similar to the form used for vertical wooden sheeting. 150. Stay Bracing. This consists of boards placed vertically against the sides of the trench and held in position by cross braces which are wedged in place. The purpose of the board against the side of the trench is to prevent the cross brace from sinking into the earth. The boards should be from 1JX4 inches to 2X6 inches and 3 to 4 feet long. The cross braces should not be less than 2X4 inches for the narrowest trenches and larger sizes should be used for wider trenches. The spacing between the cross braces is dependent on the character of the trench and the judgment of the foreman. Stay bracing is used as a precautionary measure in relatively shallow trenches with sides of stiff clay or other cohesive material. It should not be used where a tendency towards caving is pronounced. Stay bracing is dangerous in trenches where sliding has commenced as it gives a false sense of security. The boards and cross braces are placed in position after the trench has been excavated. 151. Skeleton Sheeting. This consists of rangers and braces with a piece of vertical sheeting behind each brace. A section of skeleton sheeting is shown in Fig. 104 with the names of the differ- ent pieces marked on them. This form of sheeting is used in uncertain soils which apparently require only slight support, but may show a tendency to cave with but little warning. When the warning is given vertical sheeting can be quickly driven behind the rangers and additional braces placed if necessary. The sizes of pieces, spacing and method of placing should be the same as POLING BOARDS 271 for complete vertical sheeting in order that this may be placed if necessary. 152. Poling Boards. These are planks placed vertically against the sides of the trench and held in place by rangers and braces. They differ from vertical sheeting in that the poling board is about 3 or 4 feet long. It is placed after the trench has been excavated ; not driven down with the excavation like vertical sheeting. An arrangement of poling boards is shown in Fig. 105. This type of support is used in material that will stand unsup- ported for from 3 to 4 feet in height. Its advantages lie in that no driving is necessary, thus saving the trench from jarring; no FIG. 104. Skeleton Sheeting. FIG. 105. Poling Boards. Showing Different Types of Cross Bracing. sheeting is sticking above the sides of the trench to interfere with the excavation; and only short planks are necessary. The method of placing poling boards is as follows: Excavate the trench as far as the cohesion of the bank will permit. Poling boards, 1J inch to 2 inch planks, 6 inches or more in width, are then stood on end at the desired intervals along each side of the trench for the length of one ranger. The poling boards may be held in place by one or two rangers. Two are safer than one but may not always be necessary. If one ranger is to be used it is placed at the center of the poling board. After the poling boards are in position the rangers are laid in the trench and the cross 272 CONSTRUCTION braces are cut to fit. If wedges are to be used for tightening the cross braces, the cross braces are cut about 2 inches short. If jacks are to be used the braces are cut short enough to accommo- date the jacks when closed, or adjustable trench braces may be used as shown in Fig. 106. The use of extension braces saves the labor of fitting wooden braces. With everything in readiness in the trench, the cross brace is pressed against the ranger which is thus held in place. The wedge or jack is then tightened holding the poling boards and cross brace in position. 153. Box Sheeting. Box sheeting is composed of horizontal planks held in position against the sides of the trench by vertical pieces supported by braces extending across the trench. The arrangement of planks and braces for box sheeting is shown in Fig. 106. This type of sheeting is used in material not sufficiently cohesive to permit the use of poling boards, and under such conditions that it is inadvisable to use vertical sheeting which protrudes above the sides of the trench while being driven. This sheeting is put in position as the trench is excavated. No more of the excavation than the width of three or four planks need be FIG. 106. Box Sheeting. unsupported at any one time. In Showing Different Types of Cross Bracing, placing the sheeting the trench is excavated for a depth of 12 to 24 inches. Three or four planks are then placed against the sides of the trench and are caught in position by a vertical brace which is in turn supported by a horizontal cross brace. 154. Vertical Sheeting. This is the most complete and the strongest of the methods for sheeting a trench. It consists of a system of rangers and cross braces so arranged as to support a solid wall of vertical planks against the sides of the trench. An arrangement of complete vertical sheeting i? shown in Fig. 107. This type can be made nearly water tight by the use of matched boards, Wakefield piling, steel piling, etc. Wakefield piling is made up of three planks of the same width and usually the same VERTICAL SHEETING 273 . 107. Vertical Sheeting. thickness. They are nailed together so that the two outside planks protrude beyond the inside one on one side, and the inside one protrudes beyond the two out- side ones on the other side as shown in Fig. 108. The pro- truding inside plank forms a tongue which fits into the groove formed by the protruding out- side planks of the adjacent pile. In placing vertical sheeting the trench is excavated as far as it is safe below the surface. Blocks of the same thickness as the sheeting are then placed against the bank at the middle and at the ends of two rangers on opposite sides of the trench. The ranger rest against blocks, and are held away from the sides of the trench by them. Cross braces are next tightened into position opposite the blocks to hold the rangers in place. After the skeleton sheeting is in place the planks forming the vertical sheeting are put in FIG. 108.-Wakefield Sheet P osition with a chisel ed g e cut on the Piling. lower end of the plank, with the flat side against the bank. The planks should be driven with a maul, the edge of the plank following closely behind the excavation. In relatively dry work the driving of the plank is facilitated by excavating beneath the edge as it is driven. The upper end of the sheeting should be protected by a malleable steel or iron cap to prevent brooming of the lumber. A cap is shown in Fig. 109. A sledge hammer may be used for driving when the lumber is protected. If the sheeting is to start at the surface and is to be j driven by hand, the first length should not exceed 4 feet unless a platform is erected for the driver. Succeeding lengths may be longer, the driver stand- ing on planks supported on the cross braces in the trench. Steam hammers and pile drivers are sometimes used for driving sheeting. FIG. 109. Section through Malleable Steel Driving Cap. 274 CONSTRUCTION The framework of the sheeting should be placed with a cross brace for each end of each ranger and a cross brace for the middle of each ranger. If the ends of two rangers rest on the same cross brace an accident displacing one ranger will be passed on to the next and might cause a progressive collapse of a length of trench, whereas the movement of an independently supported ranger should have no effect on another ranger. The cross braces should have horizontal cleats nailed on top of them as shown in Fig. 107 to prevent the braces from being knocked out of place by falling objects. In driving vertical sheeting a vacant place will be left behind each cross brace corresponding to the original block placed to hold the ranger away from the bank. This is an unde- sirable, feature in the use of vertical sheeting. It is ordinarily remedied by slipping in planks the width of the slot and wedging or nailing them against the convenient cross bracing. In extremely wet trenches, after all other pieces of vertical sheeting are in place, the original cleat behind the cross brace can be knocked out and a piece of sheeting slipped into this opening and driven. Care must be taken in this event not to drive the rangers down when driving the sheeting. If the bracing begins to drop, it should be supported by vertical pieces between the rangers and resting on a sill at the bottom of the trench. 155. Pulling Wood Sheeting. Wood sheeting is pulled after the completion of the trench by a device shown in Fig. 110. In wet trenches where the removal of the sheeting would permit a movement of the banks, result- ing in danger to the sewer or other structures, the sheeting should be left in place in the trench. If sufficient saving can be made the sheeting is cut off in the trench immediately above the danger line, usually the ground water line. The cutting . is done with an axe or by a power driven saw FIG. 110. Steel , . , , Clamp for Pull- devised for the purpose. ing Wood Sheet- 156. Earth Pressures. 1 The various theories ing. of earth pressure are so conflicting in their conclusions as to be confusing. Rankine's theory, the most frequently used, assumes that the pressure increases with the depth, whereas Meem's theory 2 leads 1 Earth Pressures, Old Theories and New Test Results, Eng. News-Record, Vol. 85, 1920, p. 632. 2 Trans. Am. Society Civil Eng'rs, Vol. 60, 1908. EARTH PRESSURES 275 to an opposite conclusion. The discussion following Meem's article is very illuminating. It indicates that no matter how good the theory, practical experience together with the use of generous sizes and close spacing are the best guides for bracing trenches and coffer dams. All are not possessed with the desired practical experience and some basis on which to commence work is essential. Another factor affecting computations of sizes based on theory is the tendency in practice to use the same size material for rangers and braces on any one job for all except very deep trenches and other special cases. Occasionally where there is an independent brace for each end of each ranger, the brace is made thinner, but is of the same depth as the ranger. The application of Rankine's theory of earth pressure to the computation of the sizes of rangers and braces will be shown. His formula for the active earth pressure against a retaining wall is: D , . cos 6 - Vcos 2 - cos 2 P=whcos0 cos 0+Vcos 2 6 cos 2 in which w = the weight of earth in pounds per cubic foot; h = depth in feet at point at which pressure is to be determined ; = the angle of surcharge, or the angle which the surface makes with the horizontal; < = the angle of repose of the earth. Usually taken as 33-41'=l horizontal to 1 vertical; P = the intensity of pressure in pounds per square foot on a vertical plane in a direction parallel to the surface of the ground. In studying the pressures for trenches the surface of the ground will be assumed as horizontal and the formula reduces to 157. Design of Sheeting and Bracing. The trench shown in Fig. Ill is assumed to be constructed in moist sand weighing 110 pounds per cubic foot, with an angle of repose of 30 degrees. The material used for sheeting and bracing is yellow pine. The steps 276 CONSTRUCTION taken in the design of the sheeting and bracing for this trench are, as follows: 1. Earth Pressure. Substituting the units given in the data, in Rankine's formula for earth pressures, P = 36.7/1. Because the earth has been freshly cut and will not be kept open long enough to break up the cohesiveness of the banks it is cus- tomary to reduce the assumed pressure by dividing by 2, 3, or 4, according to the natural cohesiveness of the material. The cohesiveness of sand is not great, therefore the pressure will be assumed as one-half of the amount given by the form- ula, or yi "? I m 4"x6 6x8-~. 4"x6" 6 **V [s 6 '-8- ~\ \ 6 .V >| 4"*8' 5 w 4t4lbs/sq.f& 4BI. Diagram '(% of Pressures! on Sheeting.l do. !M 1 ,. f |-4-VH 4"x8' KIO, 8x10* "FTF 2. Thickness of Sheeting and Spacing of Rangers. It is desir- able to use the same thickness of sheeting throughout the depth of the trench. Computations should therefore be commenced at the bottom of the trench where the pressures are the greatest and the thickest sheeting will be required. It is necessary to determine by trial a spacing for the rangers and a thickness of sheeting so that the sheeting is stressed to its full working strength. Having determined the thickness of the sheeting at the bottom, the remainder of the computations consists in determining the spacing of the rangers. In the example the lower ranger will be assumed as 3 feet from the bottom of the trench and the distance to the next ranger as 4 feet. FIG. 111. Diagram for the Design of Wood Sheeting. DESIGN OF SHEETING AND BRACING 277 The intensity of pressure at 22 feet 9 inches is 409.5 pounds per square foot. The intensity of pressure at 26 feet 9 inches is 481.5 pounds per square fot. The distribution of pressures is shown by the diagram on Fig. 111. The maximum bending moment is slightly below the point mid- way between the rangers and for a 12-inch strip is 10,500 inch pounds. Assuming 3 inch sheeting the maximum fiber stress is: Me 10,400X1.5X12 /=-=-= -- -- = 568 pounds per square inch. 1 \.a/\&( The working strength of yellow pine as given in Table 59, is 1200 pounds per square inch. Thinner sheeting should therefore be used. TABLE 59 WORKING UNIT STRESSES FOR TIMBER The most used value in the Building Codes of Baltimore, Boston, Cin- cinnati, Chicago, District of Columbia, and New York City Wood Tension, lb.sq.in. Com- pression With Grain, Ib.sq. in. Com- pression Across Grain, Ib.sq. in. Trans- verse Bending, Ib.sq. in. Shear With Grain, Ib.sq. in. Shear Across Grain, Ib.sq. in. Yellow pine 1200 1000 600 1200 70 500 White pine 800 800 400 800 40 250 Spruce and Va. pine. Oak 800 1000 800 900 400 800 800 1000 50 100 320 600 Hemlock 600 500 500 600 40 275 Chestnut .... 600 500 1000 800 150 Locust 1200 1000 1200 100 720 As published in American Civil Engineers Pocket Book. Assuming 2-inch sheeting, the fiber stress is 1,300 pounds per square inch. This stress is too large. By reducing the ranger spacing slightly the stress can be brought within the required limits. Assuming a ranger spacing of 3 feet 9 inches the depth to the upper ranger is changed to 23 feet and the maximum stress in the 278 CONSTRUCTION 2-inch sheeting becomes 1,140 pounds per square inch, a satis- factory result. The results for the computations for the other ranger spacings are shown in Table 60. The spacing of the rangers at the sheeting junctions is controlled by convenience and is not computed so long as it is obviously safe. 3. Size of Rangers. The rangers will be assumed as 16 feet long with two end cross braces and one intermediate cross brace for each ranger. Starting as before at the bottom of the trench. The area of the panel below the ranger and between cross braces is 24 square feet. The average intensity of pressure is 28.25X18 = 508.5 pounds per square inch. The load transmitted to the ranger is 6,000 pounds. Similarly the load transmitted to the ranger from the panel above is 6,890 pounds. The total distributed load on the ranger is 12,890 pounds. If b is the vertical dimension of the ranger and d is the hori- zontal dimension in inches, then from the beam theory, using / as 1,200 pounds per square inch, ^ 2 = o' * n w ^ c ^ M is expressed in inch pounds. The maximum bending moment is Wl 12,200X8X12 -5- = - 5 - = 155,000 inch-pounds. o o Therefore, bd 2 = 775. An 8X10 inch beam will fulfill the conditions closely. Substi- tuting these dimensions in the beam formula 155,000X5X12 ~ / 8X1000 = 1,160 pounds per square inch tension in outer fiber. The results of the computations for other rangers are shown in Table 60. 4. Size of Cross Braces. The cross braces act as columns. The dimensions of the cross braces are determined by trial in such a manner that the vertical dimension of the brace is equal to the vertical dimension of the ranger and the compressive stress in pounds per square inch is computed from the expression, Adopted by the Am. Ry. and Maintenance of Way Ass'n in 1907. DESIGN OF SHEETING AND BRACING 279 TABLE 60 COMPUTATIONS FOR SHEETING AND BRACING FOR TRENCH SHOWN IN FIG. Ill Material is moist sand weighing 1 10 pounds per cubic foot, with an angle of repose of 30. Lumber is yellow pine, with working stresses as given in Table 59. Working stresses for columns given as S ha- Sheeting 2 Inches X 12 Inches Cross Braces Maxi- Allow- Maxi- mum Actual In- able Depth mum Bending Moment, Fiber Stress, Pounds Depth and Description Total Load, Pounds Size, Inches tensity, Pounds per In- tensity, Pounds Inch- Pounds per Square Square Inch per Square Inch Inch 23'-26 . 75' 9100 1140 end at 26' 9" 6,445 4X8 202 784 19'-23' 8800 1100 int. at 26' 9" 12,890 4X8 403 784 13'-17.5' 8550 1070 end at 23' 0" 6,393 4X8 200 784 8'-13' 7160 900 int. at 23' 0" 12,785 4X8 400 784 (X-6' 3000 375 end at 19' 0" 3,930 4X8 123 784 int. at 19' 0" 7,860 4X8 246 784 end at 17' 6" 3,566 4X8 112 684 int. at 17' 6" 7,132 4X8 224 684 end at 13' 0" 4,385 4X8 137 684 int. at 13' 0" 8,770 4X8 274 684 end at 8' 0" 2,270 4X6 95 687 int. at 8' 0" 4,540 4X6 189 667 end at 6' 0" 1,344 4X6 56 584 int. at 6' 0" 2,687 4X6 112 584 end at O 7 0" 432 4X6 18 584 int. at 0' 0" 863 4X6 36 584 l Rangers Maxi- Area In- mum Maxi- Depth of Panel Below this tensity of Pressure, Pounds Total Load in Load Transmitted to the Ranger from the Size, Inches Bending Moment in Thou- mum Stress Pounds per Depth, Square per Square Pounds Panel Panel Both sand Inch- Square Inch Feet Inch Below Above Panels Pounds 26' 9" 24 508.5 12,200 6000 6890 12,890 8X10 155 1160 23' 0" 30 448 13,440 6545 6240 12,785 8X10 153 1150 19' 0" 32 378 12,100 5860 2000 7,860 8X10 94.3 708 17' 6" 12 328.5 3,942 1942 5190 7,132 8X10 85.6 636 13' 0" 36 274.5 9,880 4690 4080 8,770 8X10 105 790 8'0" 40 189 7,560 3480 1060 4,540 6X 8 54.4 850 6'0" 16 126 2,020 960 1727 2,687 6X 8 32.2 503 (XO" 48 54 2,590 863 863 | 6X 8 10.4 161 280 CONSTRUCTION in which S = permissible crushing across the grain in a column whose length is greater than 15 diam- eters; Si = unit working compressive strength of wood ; 1 = length of the column; d = smallest dimension of the column; I and d are in the same units. The lower intermediate cross brace supports a length of 8 feet of the lower ranger on which the load has been found to be 12,890 pounds. The load on the end cross brace for the same ranger is one-half of this or 6,445 pounds. The length of each brace is 4 feet 4 inches. From Table 59, Si is 1,000 pounds per square inch. From the column formula, S is 784 pounds per square inch. A 4X8 inch cross brace is the smallest that is feasible. This is stressed only 12,890 pounds or 403 pounds per square inch, which is well within the permissible limits. The results of the other computations for cross braces are shown in Table 60. 158. Steel Sheet Piling. This is coming into more general use with the increased cost of lumber and better acquaintance with its superiority over wood under many conditions. Although its first cost is higher than that of wood, the fact that with proper care it can be used almost an indefinite number of times renders it economical to contractors who may have an opportunity to make repeated use of it. The life of good yellow pine sheeting with the best of care may be as much as three or four seasons. With no particular care it will be destroyed at the first using. Fig. 112 shows various sections of steel piling used for trench sheeting. These forms are practically water tight and aid mate- rially in maintaining dry trenches. The piling can be made water tight by slipping a piece of soft wood between the steel sections when they are being driven, or by pouring in between the piles some dry material which will swell when wet. The piling is gen- erally driven by a steam hammer and is pulled by attaching a ring through a bolt hole in the pile, or by grasping the pile with a clutch that tightens its grasp as the pull increases. An inverted steam hammer attached to the pile is sometimes used in pulling it. The impulses of the hammer together with a steady pull on the cable serve to drag out the most stubborn piece of piling. LOCATING THE TRENCH 281 LINE AND GRADE 159. Locating the Trench. In order to locate a trench a line of stakes should be driven at about 50-foot intervals along the center line of the proposed sewer before excavation is commenced. Reference stakes or reference points to this line are located at some fixed offset or easily described point, or the stakes marking /~~*~j*r_: //& r > Section 15" Arched- Web Section (No.S.P.HI5) Modulus, Single = 11.80 46.5 lb. per sq.ft. of Wall 227.02 kg. per sq. meter of ,, .Interlocked. 14.11 68.12 lb. tin. ft. of Bar. 66.49 7, ' ifn. Bar. Section Modu/> 14 Arched- Web Section (No.S.RE 14) 'du/vi, Single - 7.61 3S lb. per sq.fr. of Wall. , Interlocked' 8.89 40.83/1. ,, l,n. fr. of Bar. 170. 90 kg. per so. meter of Wall. 60.76 , n Im. Bar. ( No.S.RFIS) . _ lb. persg. ft. of Wall. 60 lb lm.fr. of Bar. 234. 34 leg. per sq. mater of Wolf. 89.29 ,, /in. n Bar. ' |2|'U "straight- Web Section. "~ (Np.S.PAIZ) Section Modulus, Single - S.73 n n ' Interlocked =6.2S FIG. 112. Sections of Lackawanna Steel Sheet Piling. the center line of the trench may be driven at some constant offset distance one side of the trench, in order to avoid danger of loss or disturbance of the stakes. Grade or cut is seldom marked on the line of preliminary stakes, although the approximate cut may be indicated. For hand excavation the foreman lays out the trench from these stakes. In machine work the operator guides the machine so as to follow the line of the stakes. 282 CONSTRUCTION 160. Final Line and Grade. After the excavation of the trench has proceeded to within a foot or two of the final depth, the grade and line are transferred to markers supported over the center of the trench. The markers are horizontal boards spanning the trench and held in position either by nails driven into stakes at the side of the trench, by nails driven into the sheeting, or by weights holding the boards on the ground. Two stakes driven in the ground at the side of the trench as shown in Fig. 113 are the common method of support. If the banks are too weak to stand under the jarring of the driving of the stakes, or pavement or other causes prevent their use the horizontal cross piece may be weighted down by bricks or a bank of earth. The cross pieces are located about every 25 feet along the trench and at any con- Center'^ Line-' W f - FIG. 113. Methods for the Support of the Grade Line. venient distance above the surface of the ground. The nearer the ground the stronger the support but the greater the inter- ference with work in the trench. The center line of the sewer is marked on the cross pieces after they are set, and vertical struts are nailed on them with one edge of the strut straight, vertical, and on the center line as shown in Fig. 1. The corresponding edge should be used on all struts in order to avoid confusion. The edge is placed in a vertical position by means of a plumb bob or carpenter's level. The cut to the invert of the sewer is recorded to an even number of feet where practicable by driving a nail in the upright strut so that the top edge of the nail is at the desired elevation above the sewer, or the upright is nailed with its top at the proper number of feet above the sewer invert. The cut is marked on the upright in feet, tenths, and hundredths from the recorded point to the elevation of the invert. The inspector should watch these grade markers with care by sighting back along them to see that they are in line and have not TRANSFERRING GRADE AND LINE TO THE PIPE 283 Grade Ground Surface Grade Rod moved. In quicksand or caving material the marks may move during the setting of the pipes and the levelman should be on the job constantly. When excavation is being done by machine the depth of the excavation is controlled by the operator who maintains a sighting rod on the machine in line with the grade marks on the uprights. 161. Transferring Grade and Line to the Pipe. In transfer- ring grade and line to the sewer a light strong string is stretched tightly from nail to nail on the uprights marking the line and grade. A rod with a right angle projection at the lower end, as shown in Fig. 114, is marked with chalk or a notch at such a distance from the end that when the mark Is held on the grade cord the lower portion of the rod which projects into the pipe will rest on the invert. The pipe is placed in line by hang- ing a plumb bob so that the plumb bob string touches the grade and center line cord. These* marks are taken only as fre- quently as may be necessary to keep the sewer in line. An experienced workman can maintain the line by eye for considerable distances. Measurements should never be taken to the top of the pipe in order to determine position and grade as the variations in the diameter of the pipe may cause appreciable errors. The position and elevation of the forms for brick, concrete, and unit block sewers are located by reference to the grade line, or they may be placed under the immediate direction of the survey party, or by specially located stakes. For large sewers requiring deep and wide excavation the grade and line stakes are driven in the bottom of the trench about a foot above the finished grade. This requires the constant presence of an engineer who is usually available on work of such magnitude. 162. Line and Grade in Tunnel. In tunnels, line and grade are given by nails driven in the roof, the progress of excavation or FIG. 114. Diagram Showing the Use of the Grade Rod for Fixing the Elevation of a Sewer. 284 CONSTRUCTION the shield being followed by eye and the forms set by direct measurement to the nails. TUNNELING 163. Depth. The depth at which it becomes economical to tunnel depends mainly upon the character of the material to be excavated and on the surface conditions. In soft dry material with unobstructed working space at the surface, open cut may be desirable to depths as great as 35 or 40 feet. Tunnels are cut in rock at depths of 15 feet or less. In some very wet and running quicksand encountered in the construction of sewers for the Sani- tary District of Chicago it was found economical to tunnel at depths of 20 feet and less. Crowded conditions on the surface, expensive pavements, or extensive underground structures near the surface may make it advantageous to tunnel at shallower depths than would otherwise be economical. Winter is the best season for tunneling as the workmen are protected from the elements and labor is more plentiful. 164. Shafts. In sinking a shaft in soft material, the excava- tion is usually done by hand, the material being thrown into a bucket which is hoisted to the surface and dumped. The size of the shaft is independent of the size of the sewer and depends princi- pally on the machinery which it is necessary to lower into the tunnel. Ordinarily a shaft 6 feet in the clear is satisfactory. A method of timbering a shaft is shown in Fig. 115. Because of the timbering the shaft must be started sufficiently large at the top to finish with the desired dimensions at the bottom. This excess size is sometimes obviated by driving the sheeting at an angle to maintain the same size of shaft from top to bottom. In timbering a shaft as shown in Fig. 115 the upper frame is staked securely in position at the surface of the ground. This frame is composed of timbers fastened together in the form of a square with the ends of the timbers extending about 12 inches on all sides. The protruding ends are used to hold the frame in position. Excavation is begun inside the frame, and sheeting is driven around the outside of it as excavation progresses. Only two or three men can work advantageously at one time in these small shafts. The second frame is made up of the same size tim- bers, but all are cut off flush with the outside of the square. The SHAFTS 285 ] /2"<5ingte Sheeting outside dimensions of this frame are such as to allow sheeting to be slipped in between it and the sheeting already driven. The frame is lowered into position and supported from the upper frame by vertical struts nailed to it. The lower end of the sheeting already driven is held out from the lower frame by blocks of the thickness of the next length of sheeting. These blocks are removed as the next length of sheeting is placed and driven. The driving of the sheeting is facilitated by excavating beneath it as it descends. The sizes of sheeting and timber- ing should be computed on the same basis as that for trench sheeting except that for depths greater than 30 to 35 feet Rankine's Theory is not applicable and judgment must be relied on for computing the sizes for deep shafts. In stiff dry ma- terial the pressures will change very little as the depth increases. Sheet- ing is needed in shaft excavation in rock only to protect the work- men from falling fragments, but in sand, particularly in quicksand and in wet ground, the pressures increase directly with the depth and the sheeting should be computed accordingly. Care must be taken to prevent the formation of cavities behind the sheeting, to fill them if formed, and to see that all pieces of the sheeting and bracing have a firm bearing. It is difficult to prevent the collapse of the shaft once the movement of earth against the sheeting has commenced. Shafts are also sunk in soft ground by constructing a concrete or metal shell resting on a cutting shoe on the surface. The material inside is dug out and the shell sinks of its own or added weight. The first section of the shell may be from 5 to 10 feet long. As this section sinks other sections are added. This is called the caisson method. It is advantageous in wet ground and Section* A-A. FIG. 115. Section of Shaft Tim- bering. Abbot, Journal Western Society of Engineers, Vol. 22. 286 CONSTRUCTION when the shafts are to be left as a permanent manhole. If a permanent shaft is to be left in an excavation being braced with wood, the permanent lining should follow within 20 to 30 feet of the shaft excavation. This is done to avoid the difficulty of maintaining a great length of temporary wood shaft with the danger of collapse, or of blocks or other objects falling on the workers below. The distance between shafts is controlled by the depth and size of the tunnel, surface conditions, and the character of the material being tunneled. Except where surface conditions are crowded the shallower the cover to the tunnel the more frequent the shafts. The advantage of frequent shafts lies in the possi- bility of removing excavated material from the tunnel promptly, and in making ventilation of the tunnel easier. The saving made by the construction of numerous shafts must be balanced against the extra cost of the shafts. For the shallowest tunnels the shafts are seldom placed closer than every 500 feet. 165. Timbering. After the shaft has been excavated to the proper grade the tunnel is struck out either by cutting through the wooden sheeting or by removing portions of the caisson lining. Practically all tunnels except those in solid rock must be framed to some extent. Some of the types of frames used in tunnel construction are shown in Fig. 116. Different combina- tions of these may be used in different classes of materials. In solid rock which remains firm on exposure no timbering is neces- sary. Where the roof only need be supported and the sides are strong enough to be used for support, a timber " hitch " or frame supported on the sides of the tunnel may be used. This is suit- able for loose rock roofs with solid rock sides. Timbering such as is shown in the lower left-hand corner of Fig. 116 becomes neces- sary in extremely soft, wet, or swelling material, where the bottom and sides as well as the roof tend to push in. The remaining frame in Fig. 116 shows a form frequently used and lying between the two extremes indicated. In wet tunnels a channel may be cut in the bottom below the sill for drainage purposes as shown in this form. The needle beam method of timbering is also shown in Fig. 116. This method of timbering is used mainly near the heading because of the speed and ease with which it can be installed, but it is undesirable because of the space occupied. The distance between frames is dependent on the size of the TIMBERING 287 tunnel and the character of the material. It is seldom greater than 6 feet and the frames are sometimes placed touching each other. The size of the timbering is a matter of experience and is generally determined by the judgment of the responsible person in charge of the construction as the result of observation during the progress of the work. The sheeting between frames is called poling boards, or spiling or lagging according as it is sharpened and driven ahead of the excavation or placed after the excavation has progressed. The Needle Beam ~ \ .^^^'^^//^'/"r^. 1 !;: Longitudinal Section* p ^pSPPfP 7 Longitudinal Section Showing Poling Boards Types of Frames and Timbering for Tunnels. Transverse Section. Tunnel Bracing Showing Needle Beam Support- for Roof. FIG. 116. Types of Frames and Timbering for Tunnels. horizontal strips placed between the frames to keep them apart are called wales. In cutting out from the shaft in soft materials requiring sup- port where the width of the tunnel is the same or smaller than that of the shaft, a frame with a maximum width four thicknesses of sheeting less than the width of the tunnel is set up against the lining of the shaft. The vertical side pieces of the tunnel frame rest on the bottom frame of the shaft as a sill and are securely wedged into position. As the lining of the shaft at the top is cut away the top poling boards of the tunnel are slipped in between the cap of the first tunnel frame and the shaft frame immediately above 288 CONSTRUCTION it. The poling boards are driven with an upward pitch so that there may be room to slip the second length of boards between the next tunnel frame and the first length of boards. The placing of the side sheeting follows in a similar manner. Excavation is then started and the poling boards driven to keep pace with it. The next frame is placed in position and the previous sheeting or boards wedged out a sufficient distance to allow the advance lining to be slipped in when the wedges are removed. Waling pieces are nailed firmly between the frames to hold them in posi- tion. The various phases in the driving of a 12-foot sewer tunnel in Seattle are shown in Fig. 117. In soft or running material it may be necessary to protect the face of the tunnel by horizontal boards, called breast boards, Jt/2 Segmsnftrf Arch Lagging- ^O\ 'Phase V:! Phase'" Phase "'Phase' 3. +. 5. 6. FIG. 117v Stages of Sewer Tunneling. Eng. Record, Vol. 69, 1914, p. 195. wedged back to the last frame placed. The excavation is per- formed by removing one board at a time, excavating behind it and then replacing it in the advance position. The advance is made from the top downwards. This represents the method pursued in the most difficult material where wooden sheeting without a shield is used. The timbering during the advance may be modified in any manner that the character of the material will permit. The timbering may lag behind the excavation a dis- tance of two or more frames, or it may be omitted altogether. Heavier timbering may be necessary in soft, slipping or shattered rock. 166. Shields. Shields are used in tunneling in soft wet material and are particularly suitable for work under air pressure. They are used in rock tunnels where water is anticipated or air SHIELDS 289 pressure is used. The shields often save the expense and diffi- culty of timbering as the masonry of the sewer follows closely behind the shield. Fig. 118 shows the arrangement for a shield for tunneling in soft material in the construction of the Milwaukee sewers. The shield has an exterior diameter of 9 feet 4 inches ^ ' \v:::7::jrd^^^ 4 .Cast Iron Jack Seat 10 I i FIG. 118. Shield for Driving Milwaukee Sewer Tunnel. Eng. News-Record, Vol. 80, 1918, p. 669. and an overall length of 9 feet 8J inches. The cutting edge sec- tion is 20 inches long. The shell is made of one inch plate to the back of the jack chambers and one-half inch plate in the tail. The shield is driven by ten 60-ton hydraulic jacks. The jacks 290 CONSTRUCTION are shown in position in the figure. These jacks rest against the finished tunnel lining and serve to consolidate it at the same time that they push the shield into the material to be excavated. The face of the tunnel is cut with a pick and shovel while the jacks are removed one at a time and a new ring of lining is put in place. The lining may be temporary timbering to receive the thrust of the jacks, but it is usually desirable that the permanent lining follow immediately behind the shield. Since the shield is larger than the outside of the lining the space left by its passage should be grouted immediately after it has passed. FIG. 119. Method of Drilling and Loading Rock Tunnel Face. Courtesy, Aetna Power Co. 167. Tunnel Machines. Tunnel machines have been used successfully on sewer tunnels in soft materials, but not in rock. 1 The machines are of different types, but in general consist of a revolving cutting head, equipped with knives, and driven by an electric motor. The bearing on which the shaft for the cutting head rests is supported against the sides of the tunnel. The muck is carried away by means of a conveyor and dumped into muck cars without rehandling. Rapid progress can be made with these machines in suitable conditions. 168. Rock Tunnels. Tunnels in rock are advanced by drilling into the face as shown in diagrammatic form in Fig. 119. The 1 Tunneling Machines Successful on Detroit Sewers, Eng. News-Record, Vol. 84, 1920, p. 329. VENTILATION 291 / holes near the center are driven in at an angle towards the center and to depths from 6 to 15 feet. The harder the rock the greater the angle with the tunnel. This is called the center cut. Other holes are driven near the outer edge of the tunnel and parallel to its axis. When fired, the wedge of rock between the center cut holes is thrown back into the tunnel and a delayed explosion then throws the sides into the hole thus made. A final delay thrusting shot throws the muck so formed away from the face of the tunnel. For tunnels up to 6 or 8 feet in height the entire bore is cut out in this fashion. For larger tunnels, the upper portion called the heading, is taken out in this way, and the remainder, called the bench, is taken out by drilling and blowing holes normal to the axis of the tunnel. The amount of powder necessary in the bench holes is much less than that required in the heading. 169. Ventilation. No tunnel more than 50 feet long should be built without ventilation. A fair amount of air for ordinary conditions is 75 cubic feet of free air per minute per person in the tunnel, and double this amount for each animal. Where explosive gases are met, or under conditions where the tunnel is hot, five or six times as much air may be needed in order to cool the tunnel or to dilute the gases. In order that the air may be fresh and cool at the face of the tunnel where work is going on it should be con- ducted to the tunnel face in a pipe and blown out into the tunnel. Immediately following a blast at the face the current should be reversed so as to draw the poisonous gases out of the tunnel through the duct. The high pressure air line leading to the drills should be opened at the same time to create a current towards the face in order to accelerate the clearing of the air at the heading. The capacity of the air machines should be sufficient to exhaust four times the volume of the gases created by the explosion, in 15 minutes. This will ordinarily call for a capacity of about 4,000 cubic feet of free air per minute. If the same blower is to be used for exhausting the gases as for ventilation while work is going on, it should have a high overload capacity to care for this situa- tion. The air line should be arranged to allow for reversal of flow. The diameter of the air pipe should be determined by a study of the saving of the cost and operation of the air equipment com- pared to the increased cost of a larger pipe line. Other factors affecting the size of the pipe line to be used are: the available space in the tunnel, the temporary character of the installation, 292 CONSTRUCTION the use of the exhaust from high-pressure air machines for the purpose of ventilation, etc. Cast-iron, spiral-riveted galvanized sheet iron, and canvas pipes have been used for conducting low- pressure ventilating air. Ventilation in tunnels working under air pressure is supplied from the compressors, and the ah- is delivered near the face of the heading, except that being used in the locks. In tunnels using air drills, the air for the drills is conducted through a sep- arate pipe as it is not economical to compress the ventilating air to the pressure necessary to operate the drills. 170. Compressed Air. Compressed air is used in tunnel work to prevent the entrance of water into the tunnel and to keep the work dry. The pressure of air used is closely that of the pressure of the ground water but in a large tunnel or a tunnel with a weak roof the pressure may be somewhat lower on account of the danger of blowing through the roof. It is evident that the water pres- sure cannot be balanced at the top and the bottom of the tunnel. To balance it at the bottom makes a blow out near the top more probable. To balance the pressure at the top may leave the bottom wet. Judgment and care must be exercised during con- struction and if the pressure is balanced at or near the bottom the roof must be carefully guarded by grouting and puddling with clay, or the surface, particularly if under water, may be covered with a clay bank. If the cavities in the tunnel lining are large, sawdust can be mixed with the grout to advantage, the mixture being pumped through holes in the roof by hand or power operated force pumps. " Blows " must be carefully guarded against as they endanger the lives of the workmen and threaten the loss of the tunnel. The pressure and volume of air supplied for some large subaqueous tunnels is shown in Table 61. Labor under compressed air is arduous and dangerous with the best of safeguards. 1 Pressure more than about 43 pounds per square inch cannot be used and at this high pressure men can- not work more than four hours at a time. Little or no distress is noted at pressures less than 15 pounds. Entrance and exit to the tunnel are gained through air locks. These are sheet-iron cylinders concreted into the lining of the tunnel or shaft. Air-tight iron doors are provided at both ends, 1 Rules on Compressed-Air Work of N. Y, State Industrial Commission, Eng. News-Record, Vol. 85, 1920, p, 1225, COMPRESSED AIR 293 TABLE 61 VOLUME AND PRESSURE OF COMPRESSED AIR IN TUNNELS (American Civil Engineers Pocket Book) Maxi- Maxi- Average Tunnel mum Distance High Water Mini- mum Cover mum Air Pressure, Pounds Air Pressure, Pounds Conditions and Cubic Feet of Free Air per Minute in per to Invert, Feet per Square Square TnoVi Feet Inch incn City and South 34 42 15 in water bearing-sand. 1660 London cubic feet per minute per face. When grouted 1000 to 1300 cubic feet per minute per face Blackball 80 5 37 35 10,000 cubic feet per minute per face in open ballast for some time Baker St. and 70 18 35 28 In gravel, 3300 cubic feet of air Waterloo per minute per face. Parallel tunnel 1650 cubic feet per min. per face Greenwich 70 30 28 20 Average 83.5 per man per minute. Never less than 66.7 Battery, East 94 12 42 26 In sand. Two working faces. River, N. Y. Maximum 32,000 East River, N. Y.. 93 8 42 27 Maximum for one face 25,000 Penn. R.R. cubic feet per minute for 24 hours. Capacity of plant for 8 faces, 80,400 cubic feet per minute North River, 98 20 37 26 Maximum in gravel 10,000 cubic N. Y., Penn. feet per man per hour. Gener- R.R. ally ranged between 1500 and 5000 which open inwards towards the tunnel. On entering the lock from the outside the door to the tunnel is found tightly closed. The outside door is then closed by hand, the air valve is opened and air is admitted to the lock until the pressure on the lock side of the tunnel door equalizes that on the tunnel side and the tunnel door is swung open by hand. When the lock is open to the tunnel the pressure in the tunnel keeps the outside door closed. In order to leave the tunnel the process is reversed. Materials 294 CONSTRUCTION are passed through the lock by the lock tender or tenders who pass through the lock with the material if the pressure is low, or who manipulate the air outside of the lock if the pressure is high. If pressures of 30 to 40 pounds are being used, two or even three locks may be necessary. EXPLOSIVES AND BLASTING 1 171. Requirements. The desirable features in an explosive to be used in trenching and tunneling in rock are: (1) stability in make up so as not to deteriorate in strength or to become dangerous during storage, (2) imperviousness to ordinary varia- tions in temperature and moisture, (3) insensibility to ordinary shocks received in transportation and handling, (4) not too diffi- cult of detonation, (5) convenient form for transportation and loading and for making up charges of different weights, (6) the non-formation of poisonous gases when fired, (7) imperviousness to water and usefulness in wet holes, (8) power without bulk, etc. 172. Types of Explosives. Explosives which fill some or all these requirements can be divided into two classes, deflagrating and detonating. A deflagration is an explosion transmitted progressively from grain to grain. A detonation is a sudden dis- ruption caused by synchronous vibrations of a wave-like char- acter. The deflagrating explosives are represented by gun- powders and contractors' powders. They must be carefully tamped in the hole to develop their full power and they must be ignited by a fuse or flame. They are valueless in water or moist holes. These powders are used mainly for loosening frozen earth, soft sandstone, cemented gravels and similar materials where a thrusting action rather than a disruption is desired. The detonat- ing explosives are most commonly represented by the dynamites. These are exploded by a shock usually caused by another explosive which has been ignited by a fuse or electric spark, and which is known as the " detonator." Detonating explosives are more powerful than deflagrating explosives and are used in all but the softest materials. 1 Taken mainly from the Engineer Field Manual of the U. S. Army; Safety Factors in the Use of Explosives by W. O. Snelling, Technical Paper No. 18, U. S. Bureau of Mines; and an article in Eng'g and Contracting, Vol. 52, 1919, p. 585. TYPES OF EXPLOSIVES 295 Gunpowder. This is a mechanical mixture of sulphur, char- coal, and saltpeter generally in the proportions of 10 parts sulphur, 15 parts charcoal, and 75 parts saltpeter (sodium nitrate). It weighs about 62J pounds per cubic foot and produces about 280 times its own volume in gas at a pressure of 4.68 tons per square inch at a temperature of 32 degrees F., which amounts to a pres- sure of approximately 38 tons per square inch at the temperature of explosion of 4,000 degrees F. Blasting Powder. This is a mixture of 19 parts sulphur, 15 parts charcoal, and 66 parts saltpeter. These powders are made in different size angular polished grains, from the size of a pin head to sizes just passing a f to \ inch hole. The larger the grains the slower the action of the powder. Nitro-Substitution Compounds. These compounds are formed by the action of nitric acid on hydro-carbons. Triton, T.N.T., or trinitrotoluene, made famous during the war, is an example of these compounds. It is made by the successive nitration of toluene, a coal tar derivative. It melts at 80 degrees C., is very stable, and is of great explosive strength. It is manufactured in a convenient form, being compressed into blocks about 2 inches square by about 4 inches long with a specific gravity of about 1.5. The blocks are usually copper plated to protect the T.N.T. from moisture. The more dense it is the less its sensitiveness. It is also put up in crystalline form in cartridges like dynamite, in which condition it is practically equal to 40 per cent dynamite. It can be cut with a knife, pounded with a hammer, and will burn freely and slowly in small quantities in the open air without exploding. It is suitable for all but the hardest rocks. It creates poisonous gases on detonation which are quickly dissipated in the open air but which render it unsuitable for use in tunnel work. Nitro-glycerine. This is formed by the action of nitric and sulphuric acids on animal compounds such as gelatine or glycerine. Nitro-glycerine is a yellowish, oily, highly unstable explosive liquid with a specific gravity of about 1.6. It will burn quietly when ignited in the open air. It will freeze at 41 degrees F., and will explode at 388 degrees F., or on concussion at a lower tempera- ture. It develops about 1,500 times its volume in gas, which due to the heat of combustion is increased to about 10,000 times its volume. It is a very dangerous explosive to handle, and is unsuit- able for use in the liquid form. 296 CONSTRUCTION Blasting Gelatine. This is made by soaking guncotton in nitre-glycerine. Gelatine dynamite, is a combination of blasting gelatine and an absorbent. Forcite is a gelatine dynamite in which the blasting gelatine, forming 50 per cent of the compound, contains 90 per cent nitro-glycerine and 2 per cent guncotton; and the absorbent, forming the other 50 per cent of the compound, contains 76 per cent of sodium nitrate, 3 per cent sulphur, 20 per cent of wood tar, and 1 per cent of wood pulp. Blasting gelatine is packed in a jelly-like mass in metal lined wooden boxes. It is less sensitive than straight dynamite and is one of the most powerful explosives known. It can be made up to equal 100 per cent dynamite. It is suitable for use in the hard- est rocks and for subaqueous work as it is not affected by moisture. It is suitable for use in tunnels as the amount of carbon monoxide, peroxide of nitrogen, hydrogen sulphide and other dangerous gases is comparatively low when fully detonated. Gelatine dynamite 1 is sold as 30 per cent to 70 per cent dynamite, the actual percentage of nitro-glycerine being less than the nominal quantity given. Dynamite. The dynamites are made by soaking nitro-glycerine in some absorbent. If the absorbent is some neutral substance such as infusorial earth the combination is known as a true dyna- mite. The false or active dynamites are those in which the absorb- ent is also an explosive compound. The false dynamites form the best known contractors' explosives. Among the materials mixed with the nitro-glycerine are: magnesium carbonate, sulphur, wood meal, wood pulp, wood fiber, wood tar, nut galls, kieselguhr, sawdust, resin, pitch, sugar, charcoal, and guncotton. The strength of dynamites is noted by the per cent of nitro-glycerine and nitro substitutes contained. Dualin and Hercules powder both contain 40 per cent nitro-glycerine. Dualin contains 30 per cent sawdust and 30 per cent potassium nitrate, but the Hercules powder, which is stronger, contains 16 per cent sugar, 3 per cent potassium chlorate, 31 per cent potassium nitrate, and 10 per cent magnesium carbonate. Dynamite is the most common explosive used on construction work. It is supplied in cylindrical sticks wrapped in paper, the diameter of the sticks varying between | and 2 inches. They are about 8 inches long. Forty per cent dynamite is the common 1 See paper by C. T. Hall before Am. Inst. Chemical Engineers. PERMISSIBLE EXPLOSIVES 297 strength found on the market. It is suitable for ordinary work in all but very hard rocks or very soft material. Direct contact with water separates the nitro-glycerine from the base and is dangerous when the explosive is used in wet places unless it is fired immediately after the hole is loaded. It freezes at about 42 degrees F., or at even higher temperatures and in the frozen state it is highly dangerous, requiring powerful detonators for firing, but exploding spontaneously from a slight jar, or the breaking of the stick. Special low-freezing dynamites are made that will not freeze above 35 degrees F. Ammonia Compounds. Ammonia dynamite is a combination of nitro-glycerine, ammonium nitrate and such other ingredients as sodium nitrate, calcium carbonate and combustible material. This form of explosive is advantageous for underground work because, like gelatine dynamite, its explosion does not create large quantities of poisonous gases. It has a low freezing point and is relatively low in cost. It is seriously affected by moisture, however, and can not be used in wet places. Ammonium nitrate explosives which do not contain nitro-glycerine include 70 per cent to 95 per cent ammonium nitrate and some combustible material. Ammo- nal is a special type of this class formed by a mixture of ammo- nium nitrate, aluminum, and triton. All of these explosives are deliquescent, insensitive to shock, and are cheaper than the dyna- mites. 173. Permissible Explosives. As specified by the United States Bureau of Mines explosives whose rapidity, detonation, and temperature of explosion will not ignite explosive mixtures of pit gases and air are known as permissible explosives. They include nitrate explosives, ammonia dynamite, and others. Gunpowder, triton, picric acid, blasting gelatine, dynamite, guncotton, etc., are not classed as permissible explosives. 174. Strength. The relative weights for equal strength of various explosives are given in Table 62. 175. Fuses and Detonators. The explosion of gunpowder and other deflagrating explosives is caused by the 'direct application of a flame led to the charge by a powder fuse, or they may be fired by a blasting cap which is itself exploded by the heat from a fuse or an electric spark. The powder fuse is a cord made up of a train of powder securely wrapped in a number of thicknesses of woven cotton or linen threads and usually made water-proof. CONSTRUCTION TABLE 62 RELATIVE WEIGHTS OF EXPLOSIVES WITH THE SAME STRENGTH AS A UNIT WEIGHT OF 40 PER CENT DYNAMITE Explosive Relative Weight Explosive Relative Weight Picric acid 0.86 Triton 0.86 Gun powder (well tamped) . 3.10 Blasting gelatine 0.43 Straight dynamite, 15%. ... 1.45 Gelatine dynamite, 30%. . . 1.28 Straight dynamite, 20 .... 1.33 Gelatine dynamite, 35 1.21 Straight dynamite, 25 .... 1.28 Gelatine dynamite, 40 ... 1.14 Straight dynamite, 30 .... 1.18 Gelatine dynamite, 50 1.04 Straight dynamite, 35 .... 1.07 Gelatine dynamite, 55 ... 0.97 Straight dynamite, 40 .... 1.00 Gelatine dynamite, 60 ... 0.90 Straight dynamite, 45 .... 0.93 Gelatine dynamite, 70 0.83 Straight dynamite, 50 .... 0.86 Straight dynamite, 55 .... 0.83 Ammonia dynamites are Straight dynamite, 60 .... 0.78 the same as gelatine dynamites Low-freezing dynamites are Chlorates (sprengle) the same as straight Rack-a-rock 1.33 dynamites Guncotton 0.72 Smokeless powder, well tamped 0.74 Ordinary fuse burns at about 2 feet per minute but there may be wide variations from this rate due to the quality of the fuse, moisture, temperature, or pressure. Moisture tends to retard the rate, pressure to increase it. Instantaneous fuse will burn at about 120 feet per second. It is distinguished from the ordinary safety fuse both by eye and touch due to the rough red braid with which it is covered. It is used in firing a number of charges simultaneously. Powder fuses are lighted by the application of a flame or smoldering torch to the freshly cut or opened end expos- ing the powder grains. Cordeau Bickford is lead tubing filled with triton, in which the flame travels at about 17,000 feet per second. This is also used for igniting charges simultaneously. The detonation of an explosive is caused by the shock or heat of the explosion of a more sensitive substance which has been exploded by a powder fuse or electric spark. The common method of detonating explosive charges is by the firing of a blast- FUSES AND DETONATORS ing cap. These caps are copper cylinders, closed at one end, about 1J inches long and J to | of an inch in diameter, or larger. They contain a mixture of about 85 per cent fulminate of mercury and 15 per cent potassium chlorate held in place by a wad of shellac, collodion, or paper. The strength of detonators is based on the weight of fulminate of mercury and is designated as shown in Table 63. TABLE 63 STRENGTH OF BLASTING CAPS Grains Grains Blasting Cap, Fulminate Electric Cap, Fulminate Commercial Grade of Commercial Grade of Mercury Mercury 3X or Triple 8.3 Single strength 12 3 4X or Quadruple 10.0 Double strength 15.4 5X or Quintiple 12 3 Triple strength 23 1 6X or Sextuple 15.4 Quadruple strength 30 9 7X or Number 20 23.1 8X or Number 30 30.9 The force of the explosion is markedly affected by the strength of the caps, the effect being greater for low-grade powders. For 40 per cent dynamite the explosion caused by a 5X cap is 15 per cent stronger than that caused by a 3X cap. For 60 per cent dynamite the difference is only 6 per cent. The deterioration of the caps will reduce the strength of an explosion noticeably. With straight dynamite, 3X caps are generally used, but with gelatine dynamite 6X or heavier caps must be used. Caps may be tested by exploding them in a confined space and noting the report and the effect on the shell. A full strength cap will tear the shell into minute pieces, while a deteriorated cap will merely tear it into three or four large pieces. An ordinary blasting cap is shown in Fig. 120 together with other equipment for blasting. Firing by electricity is generally safer and more satisfactory than by the use of ordinary caps and powder fuses. The explosion is more certain and its exact time is under the control of the opera- tor. Fig. 121 shows a section through an electric blasting cap or 300 CONSTRUCTION detonator, commonly called an electric fuse. Delayed-action electric detonators are made by inserting a slow-burning sub- stance between the platinum bridge and the detonating substance. The time of delay is controlled by the depth of the slow -burning substance. Delayed-action detonators are useful in tunnel work where it is desired to explode the charge in three or four stages in order that the debris from one charge may be out of the way of the following, and that the forces of the explosions may not serve to nullify each other. 176. Care in Handling. Some of the don'ts in the handling MAGNETO DYNAMI1E .CARTRIDGES POWDER ELECTRI CAPS CLECTRK FUSE BLASTING CAPS FIISE REEL FUSE ELECTRIC WIRE CAP CRIMPERS SAFETY' RESISTANCE x GALVANOMETER FUSE COIL FIG. 120. Blasting Supplies. Courtesy, Aetna Powder Co. of explosives recommended by the U. S. Army Engineer Field Manual are : in the use of nitro-glycerine explosives of all kinds (a) Don't store detonators with explosives. Detonators should be kept by themselves. (6) Don't open packages of explosives in a store house. (c) Don't open packages of explosives with a nail puller, pick or chisel. Packages should be opened with a hard wood wedge and mallet, outside of the magazine and at some distance from it. (d) Don't store explosives in a hot or damp place. All explosives spoil rapidly if so stored. (e) Don't store explosives containing nitro-glycerine so that the cartridges stand on end. The nitro-glycerine is more likely to leak from the cartridges when they stand on end than it is when they lie on their sides. CARE IN HANDLING 301 (/) Don't use explosives that are frozen or partly frozen. The charge may not explode completely and seri- ous accidents may result. If the explosion is not complete the full strength of the charge is not exerted and larger quantities of harmful gases are given off. (g) Don't thaw frozen explo- sives in front of an open fire, nor in a stove, nor over a lamp, nor near a boiler, nor near steam pipes, nor by placing cartridges in hot water. Use a commercial or improvised thawer. (h) Don't put hot water or steam pipes in a magazine for thawing purposes. (i) Don't carry detonators and explosives in the same package. Detonators are extremely sensitive to heat, friction, or blows of any kind. (.7) Don't handle detonators or explosives near an open flame. (k) Don't expose detonators or explosives to direct sunlight for any length of time. Such exposure may increase the danger in their use. (I) Don't open a package of explosives until ready to use the explosive, then use it promptly. (m) Don't handle explosives carelessly. They are all sensitive to blows, friction, and fire. (ri) Don't crimp a detonator (blasting cap) around a fuse with the teeth. Use a cap crimper, which is supplied for this purpose. (o) Don't economize by using a short length of fuse. (p) Don't return to a charge for at least one-half hour after a miss fire. Hang fires are likely to happen. (q) Don't attempt to draw nor to dig out the charge in case of a miss fire. Some of the positive rules in connection with the handling of explosives are : build the magazine on an earth foundation remote from any other structures, protect it with earth embankments that will direct the force of the explosion upwards, and build it of materials that will supply as few missiles as possible. Hollow tile brick, double- walled galvanized iron filled with sand, and similar constructions are satisfactory. The magazine may be - Electric Leads Copper Shell [.Sulphur Filling -Sulphur Plug --Platinum Bridge -Guncotton or Loose Mercury Fulminate -Mercury Fulminate Packed FIG. 121. Electric Fuse. Full size. 302 CONSTRUCTION heated by steam or hot-water pipes so located that explosives can- not come in contact with them, or by a cluster of incandescent bulbs, but if the explosives become frozen they must not be thawed out by turning on the steam or hot water. If powder or nitro- glycerine is dropped on the floor the magazine should be emptied, washed out with a hose and spots of nitro-glycerine scrubbed with a brush and a mixture of J gallon of wood alcohol, J gallon of water and 2 pounds of sodium sulphide. Frozen explosives may be thawed by spreading out on special shelves in a warm thaw house not in the magazine proper, by burying in a manure pile so that the explosive may not become moistened, or more com- monly by heating slowly in a water bath. This is a dry kettle in which the explosives are placed and covered. The kettle is then put in another containing water which is heated gently to about 120 degrees F. It should not be boiled. In case of a miss fire, instead of digging out the old charge put a new charge on top of the old and fire the two simultaneously. 177. Priming, Loading, and Firing. Priming is the act of placing the cap or detonator in the cart- ridge of explosive. The primer is either the cap or the cap and cartridge which are to be detonated by the fuse. If a cap and safety fuse are to be used the paper at the upper end of the cartridge is opened, a hole is poked in the explosive with the finger or a piece of wood, the cap and the attached fuse are pushed into the hole and gently embedded in the explosive so that the end of the cap is exposed sufficiently to prevent the fuse from igniting the dynamite directly. The paper is then folded up and tied firmly around the fuse with a piece of string. The result is shown in Fig. 122. In placing the fuse in the cap the end of the fuse is cut off square, and inserted in the open ar en< ^ ^ ^ e ca P' care being taken not to spill the Safety Fuse, loose grains of powder or to grind the fuse down and Cap. on top of the cap. When the fuse is shoved firmly into place the upper portion of the copper cap is pressed or crimped with the cap crimpers shown in Fig. 120. The number of primers to be used is dependent on the size FIG PRIMING, LOADING, AND FIRING 303 and location of the charge, but in practically all sewer work only one primer is used to each hole. In bulky charges the primer should be placed near the center of the charge and the fuse so protected that it will not ignite the charge prematurely. In drill holes the primer is put in last with the cap end down. In loading a hole, it is first pumped and cleaned out. This can be done satisfactorily with the end of a stick frayed out into a broom. Cartridges which very nearly fill the hole are dropped in one at a time and are pressed firmly together, with a light wooden tamping bar. They should not be pounded. After the primer is placed, a wad of clay or similar material is pressed gently into the hole against it and the hole is then filled with well-tamped clay. In tunnel work tamping is not so essential as an overcharge of powder is usually used and the time of tamping, which is worth more than two or three sticks of dynamite, is saved. In handling bulk explosives, such as gunpowder, they are poured into the hole, the fuse is set in the upper portion and the remainder of the hole is tamped with clay as for dynamite cartridges. If a large number of charges are to be fired simultaneously with a safety fuse, the length of the fuse to each charge should be made equal or a safety fuse used to a common center and approxi- mately equal lengths of instantaneous fuse or Cordeau Bickford used from there to FIG. 123. Methods for Cutting Safety Fuse for the charge. In splic- Splicing, ing the fuses for such connections they are cut diagonally as shown in Fig. 123 and bound together firmly with tape. Electric connections are particularly advantageous under such conditions as they avoid the dangers incidental to spliced fuses and are less expensive. In tunnel work simultaneous electric detonation is not desirable as the holes should be fired progressively: 1st, the cuts; 2nd, the relievers; 3rd, the backs; 4th, the sides; and 5th, the lifters. Different lengths of safety fuse, or delayed action electric fuses can be used for these delay shots. In igniting a safety fuse an open flame such as that furnished by a match or candle is the most satisfactory. For electric fuses 304 CONSTRUCTION the current is generated by a magneto shown in Fig. 120. Pressing vigorously down on the handle closes the circuit and generates an electric current which heats the platinum bridges and explodes the charges. For the small number of charges used in ordinary construction they are connected in series so that if there is a broken connection anywhere no charge will be exploded. If many charges are to be fired and a line circuit is to be used, the final connection should not be made until just before the charge is to be fired in order to obviate the danger of stray currents firing the charge prematurely. Care should be taken to see that all connections are good and that there are no broken wires on the line. 178. Quantity of Explosive. The quantity of explosive to be used can be determined satisfactorily only by experience on the job in question, as the factors affecting the necessary quantity are so diverse. The figures in Table 64 indicate the relative amounts needed under different conditions. PIPE SEWERS 179. The Trench Bottom. It is customary to dig the bottom of the trench to conform to the shape of the lower 45 degrees to 90 degrees of the sewer if the character of the material will allow such construction. In soft material which will not hold its shape the sewer may be encased in concrete or a concrete cradle may be prepared for the pipe. In rock the trench is excavated to about 6 inches below grade and refilled with well- tamped earth so as to form a cradle giving bearing to 60 to 90 degrees of the pipe circumference. For large sewers to be con- structed in the trench special foundations are sometimes built. 180. Laying Pipe. Before the pipe is lowered into the trench the sections which are to be adjacent should be fitted together on the surface and the relative positions marked by chalk so that the same position can be obtained in the trench. Small pipes are lowered into the trench and swung into posi- tion on a hook as shown in Fig. 124. Pipes up to 15 or 18 inches in diameter can be handled by the pipe layer and helper in the trench without assistance. Heavier pipes may be lowered into the trench by passing ropes around each end of the pipe. One end of the rope is fastened at the surface and the ropes are paid out by the men at the surface as the pipe is lowered. If the pipes QUANTITY OF EXPLOSIVE 305 - i J $ H a I .-s e d o3 P- 3 ^2 o o I S OOOOQ^OQ^QJC^OOC^OQ^O vO oooooooooooooooS p p t>-io i-iCQ d i-i 38 ;3Sa888888888S ; d i-i : dddo'di-i^di-idcJ'-id O CO o^ - | i : III 306 CONSTRUCTION have been fitted together and marked at the surface it is undesir- able to use this method of lowering as the position in which the pipes arrive in the bottom of the trench can not be easily pre- dicted. A cradle may be used for shoving the pipe into position as is shown in Fig. 125. Pipes above 24 to 27 inches in diameter are too large to be handled from the side of the trench. A hook as shown in Fig. 124 is placed in the pipe so that it will be in the proper position when lowered. It is raised by a rope passing through a block at the peak of a stiff-legged derrick which spans the trench, or by a crane. If a derrick is used the rope passes to a windlass on the opposite side of the trench from the pipe. Mechanical FIG. 124. Hook for Lowering and FIG. 125. Cradle for Placing Placing Sewer Pipe. Sewer Pipe. power may be used for raising pipes too heavy to be raised by hand. The pipe is then lowered and swung into position while sup- ported from the derrick. Excessive swinging is prevented by holding back on the guide rope as the pipe is raised and lowered. Pipes are usually laid with the bell end up grade as it is easier to fit the succeeding pipe into the bell so laid and to make the joint, particularly on steep grades. The Baltimore specifica- tions state: The ends of the pipe shall abut against each other in such a manner that there shall be no shoulder or unevenness of any kind along the inside of the bottom half of the sewer or drain. Special care should be taken that the pipe are well bedded on a solid foundation The trenches where pipe laying is in progress shall be kept dry, and no pipe shall be laid in water or upon a wet bed unless especially allowed in writing by the Engineer. As the pipe are laid throughout the work they must be thoroughly cleaned and protected from dirt and water, no water being allowed to flow in them in any case during the construction except such as may be permitted in writing by the Engineer. No length of pipe shall be laid until the preceding length has been thoroughly embedded and secured in place, so as to prevent any movement or disturbance of the finished joint. / JOINTS 307 The mouth of the pipe shall be provided with a board or stopper, carefully fitted to the pipe, to prevent all earth and any other substances from washing in. 181. Joints. Pipes may be laid with open joints, mortar joints, cement joints, or poured joints. Open joints. are used for storm sewers in dry ground close to the surface. Mortar and cement joints are commonly used on all sewers except in special cases. Cement joints are more carefully made than mortar joints and result in a greater percentage of water-tight joints. Poured joints are used in wet trenches where it is necessary to exclude ground water from the sewer. A specification used in some cities for open joints is: Pipes laid with open joints are to be laid with their inverts in the same straight line and shall be firmly bedded throughout their length on the bottom of the trench. No cement or mortar is to be used in the joints. Not more than | inch shall be left between the spigot end of the pipe and the shoulder of the hub of the pipe into which it fits. The joints shall be surrounded with cheese cloth, burlap, broken pipe, gravel or broken stone. The purpose of the cheese cloth, etc., is to prevent fine earth from sifting into the pipe until the cheese cloth or other material has rotted away, by which time the earth has become arched over the opening. Mortar joints are specified by Metcalf and Eddy as follows: Before a pipe is laid the lower part of the bell of the preceding pipe shall be plastered on the inside with stiff mortar of equal parts of Portland cement and sand, of sufficient thickness to bring the inner bottoms of the abutting pipe flush and even. After the pipe is laid the remainder of the bell shall be thoroughly filled with similar mortar and the joint wiped inside and finished to a smooth bevel outside. In some work a wood block or a stone is embedded in the mor- tar at the bottom of the joint to bring the spigot in place concen- tric with the next pipe. Cement joints are specified in the Baltimore specifications as follows: Cement joints shall be made with a narrow gasket of hemp or jute and cement mortar, and special care shall be taken to secure tight joints. The gasket jshall be soaked 308 CONSTRUCTION in Portland cement grout and then carefully inserted between the bell and the spigot, and well calked with suitable hardwood or iron calking tools. It shall be in one continuous piece for each joint, and of such thickness as to bring the inverts of the two pipes smooth and even. The remainder of the joint shall be filled with cement mortar all around, on the bottom, top and sides, applied by hand with rubber mittens, well pressed into the annular space and beveled off from the outer edge of the bell to a dis- tance of two inches therefrom, or to an angle of 45 degrees. The inside of each joint shall be thoroughly cleansed of all surplus mortar that may squeeze out in making the joint; and to accomplish this some suitable scraper or follower, or form shall be provided and always used immediately after each joint is finished. Cement joints so made, form the most satisfactory joint for ordinary conditions and are the most frequently used. They are not always water-tight and can be penetrated by roots. Some roots are able to penetrate holes of almost microscopic size and to form growths in the sewer or to split the joints. Poured joints are made by pouring some jointing compound, while in a fluid state, into the joint in which it hardens, thus seal- ing the joint. Water-tightness in sewer lines to exclude ground water has also been attempted by using the ordinary cement joint and surrounding the pipe with a layer of cement or concrete. This has not always been successful as it is difficult to obtain the proper class of workmanship in wet sewer trenches. The requisite qualities of a poured jointing material are: (1) It should make a joint proof against the entrance of water and roots. (2) It should be inexpensive. (3) It should have a long life. (4) It should not deteriorate in sewage which may be either acid or alkaline. (5) It should adhere to the surface of the pipe. (6) It should run at a temperature below about 400 F., as too high temperatures will crack the pipe. (7) It should neither melt nor soften at temperatures below 250 F. in order to maintain the joint if hot liquids are poured into the sewer. (8) It should be elastic enough to permit slight move- ments of the pipes. (9) It should not require great skill in using as it must be handled ordinarily by unskilled workers. JOINTS 309 / The materials used for poured joints are: cement grout; sulphur and sand; and asphalt or some bituminous compound made of vulcanized linseed oil, clay, and other substances the resulting mixture having the appearance of vulcanized rubber or coal tar. The bituminous materials most nearly approach the ideal conditions. Cement grout is made up of pure cement and water mixed into a soupy consistency. Its main advantages are its cheapness and ease in .handling in wet trenches or difficult situations. The result is no better than a well made cement joint. There is no elasticity to the joint and a movement of the pipe will break it. Sulphur and sand are inexpensive, comparatively easy to handle, and make an absolutely water-tight and rigid joint which is stronger than the pipe itself. It frequently results in the crack- ing of the pipe and is objected to by some engineers on that account. In making the mixture, powdered sulphur and very fine sand are mixed in equal proportions. It is essential that the sand be fine so that it will mix well with the sulphur and not precipitate out when the sulphur is melted. Ninety per cent of the sand should pass a No. 100 sieve and 50 per cent should pass a No. 200 sieve. The mixture melts at about 260 F. and dees not soften at lower temperatures. For making a joint in an 8 inch pipe about 1J pounds of sulphur, 1^ pounds of sand, \ pound of jute, and 0.4 pound of pitch are used. The pitch is used to paint the surface of the joint while still hot in order to close up any possible cracks. Among the better known of the bituminous joint compounds are: " O.K." Compound made by the Atlas Company, Mertz- town, Pa., Jointite and Filtite, manufactured by the Pacific Flush Tank Co., Chicago and New York, and some of the products of the Warren Brothers Co., Boston. These compounds fill nearly all of the ideal conditions except as to cost and ease in handling. They are somewhat expensive and if overheated or heated too long become carbonized and brittle. In cold weather they do not stick to the pipe well unless the pipe is heated before the joint is poured. On some work joints have been poured under water with these compounds, but success is doubtful without skillful handling. An overheated compound will make steam in the joint causing explosions which will blow the joint clean, 310 CONSTRUCTION and an underheated compound will harden before the joint is completed. The materials should be heated in an iron kettle over a gaso- line furnace or other controllable fire, until they just commence to bubble and are of the consistency of a thin sirup. Only a sufficient quantity of material for immediate use should be pre- pared and it should be used within 10 to 15 minutes after it has become properly heated. The ladle used should be large enough to pour the entire joint without refilling. There are other important points to be considered in pouring joints which can be learned best by experience. The quantity of material necessary for making these joints, as announced by the manufacturers, is shown in Table 65. TABLE 65 QUANTITY OF COMPOUND NEEDED FOR POURED JOINTS Quantity of Material in Pounds per Joint Diameter of Pipe, Standard Socket Deep and Wide Socket in Inches Jointite Filtite O.K. Jointite Filtite O.K. 6 0.82 0.72 0.42 1.46 1.28 0.72 8 1.06 0.95 0.73 1.82 1.60 1.25 10 1.30 1.15 0.89 2.26 1.98 1.52 12 2.08 1.82 1.42 2.65 2.32 1.80 15 2.52 2.20 1.74 3.20 2.80 2.20 18 3.02 2.64 2.58 3.75 3.29 3.25 20 3.44 3.00 2.86 4.30 3.78 3.60 22 3.62 3.16 3.13 4.62 4.07 3.97 24 4.03 3.50 3.41 4.91 4.31 4.27 In making a poured joint the pipes are first lined up in posi- tion. A hemp or oakum gasket is forced into the joint to fill a space of about f of an inch. An asbestos or other non-combustible gasket such as a rubber hose smeared with clay is forced about J inch into the opening between the bell and the spigot and the compound is poured down one side of the pipe through a hole broken in the bell, until it appears on the other side, and the hole THE INVERT 311 / is filled. Occasionally the non-combustible gasket is wrapped tightly around the spigot of the pipe and pressed or tied firmly to the bell. In pouring cement grout joints a paper gasket is used which is held to the bell and spigot by draw strings. Greater speed in construction and economy in the use of materials are obtained by joining two or three lengths of pipe on the bank and lowering them into the trench as a unit. The pipes are set in a vertical position on the bank with the bell end up, one length resting in the other. The joint is calked with hemp and poured without the use of the gasket. The joint should always be poured immediately after being calked so that the hemp can not become water soaked. The asbestos gasket should be removed as soon as possible after the joint is poured in order to prevent sticking with resultant danger of breaking of the joint when attempting to pull the gasket free. One man can pour about 33 eight-inch joints, and two men can complete about 26 twelve-inch joints per hour on the bank where conditions are more or less fixed. 182. Labor and Progress. The labor required for the laying of pipe sewers, exclusive of excavation, bracing and backfilling, consists of pipe layers and helpers. For pipes 24 to 27 inches in diameter or smaller one pipe layer and one or more helpers are necessary, dependent on the size of the pipe and the depth of the trench. For larger pipes two pipe layers can work econom- ically each working on one-half of the pipe and making half of the joint. The speed of pipe laying is ordinarily limited by the speed of the excavation, but on a job in Topeka, Kan., 1 where the average day's progress with a machine excavator was 200 to 500 feet of trench per day, the pace was limited by the speed of the pipe laying gang. This gang consisted of two pipe layers in the trench and two helpers on the surface. The sizes of pipes handled were from 8 to 27 inches. BRICK AND BLOCK SEWERS 183. The Invert. In good firm ground the excavation is cut to the shape of the sewer and the bricks are laid directly on the ground, being embedded in a thick layer of mortar. After the foundation has been prepared and before the bricks are laid, 1 Eng. News, Vol. 75, 1916, p. 592. 312 CONSTRUCTION two wooden templates, called profiles, are prepared, similar to that shown in Fig. 126, to conform to the shape of the inside and outside of the sewer. Each course of bricks is represented by a row of nails in the profile and each nail corresponds to a joint in the row. The two profiles are set true to line and grade. A cord is stretched tightly between the two lowest nails on opposite templates and a row of bricks is laid. The bricks are laid radially and on edge with their long dimension parallel to the axis of the sewer and with one edge just touching the string. As each one or two or three rows are completed the guide line is moved up to the next nails. When the bricks are laid on the ground all but large depressions are filled in with tamped sand or mortar by the masons. Approximately the same number of rows of bricks is kept com- pleted on either side of the center line. The FIG. 126. Profile for succeeding courses follow within three to five Brick Sewers. rows of each other, the only bond between courses being the mortar joint. This is called row lock bond and with few exceptions has been used on all brick sewers in the United States. As the sides of the sewer become higher during the construction, platforms must be built for the masons. These platforms are built of wood and rest directly on the green brickwork. They should be designed to spread the load as much as possible. The brickwork of the invert is continued up in this way to the springing line. As soon as one section is completed one profile is moved 10 to 20 feet ahead along the trench according to the standard length of sections, and set in position. The line is then strung from it to nails driven or pushed into the cement joints of the last completed section. Between work done on separate days the bricks are racked back in courses to provide a satisfactory bond. In ground too soft to support the brickwork directly a cradle is prepared by placing profiles in position in the sewer and nailing 2-inch planks to these profiles, first firmly tamping earth under the planks. The bricks are laid in this cradle in a manner similar to that explained for sewers with a firm foundation. In still softer ground it may be necessary to construct a concrete cradle to support the bricks. 184. The Arch. The arch centering consists of a wooden form made up of wooden ribs as shown in Fig. 127. The center BLOCK SEWERS 313 conforms to the shape of the inside of the arch with allowance for the thickness of the lagging. The lagging is nailed on the ribs in straight strips parallel to the axis of the sewer. The center is supported on triangular struts resting against the sides and on the bottom of the sewer and is lifted into position by wedges driven between it and the support. The centers may be placed immediately after the completion of the invert, or a day or two may be allowed to pass to give the invert an opportunity to set. After the centers are fixed in place the arch brick are carried up evenly on each side and are pounded firmly into place. The center is usually, but not always " struck " immediately, and the arch brick are cleaned and pointed up from the inside. The outside is cov- ered with a layer of J to f of an inch of cement mortar and may be backfilled to the top of the arch in order to maintain the moisture of the FIG. 127. -Centering for Brick Sewer, mortar during setting and to press the bricks of the arch together firmly. The centers are some- times made collapsible so that they can be carried or rolled through the finished brickwork to the advanced position. In " striking " the centers the wedges are removed and the wings folded in. In tunneling, the invert of the sewer is constructed in the same fashion as for open-cut work. The arch centering is made in short sections and the bricks are put in position by reaching in over the end of the centering. All of the timbering of the tunnel is removed except the poling boards or lagging against which the bricks or mortar are tightly pressed, the boards being bricked in permanently. 185. Block Sewe'rs. Sewers made of unit blocks of concrete or vitrified clay are constructed in a similar manner to brick sewers. Fig. 128 shows the construction of a block sewer at Clinton, Iowa. In this sewer there are two rings; an inside one of solid blocks and an outside one of hollow blocks. Block sewers do not demand the skill in construction that is demanded by brick sewers, as the blocks are so cast that the joints are radial, whereas only experienced masons can lay bricks radially. 314 CONSTRUCTION 186. Organization. The number of men employed on a brick or block sewer is proportioned according to the size of the sewer and the working conditions. The number of men working on different tasks usually bears the same ratio to the number of masons employed, regardless of the size of the work. These proportions are shown for different jobs, in Table 66. 187. Rate of Progress. In a general way it can be assumed that the lay- ing of 1,000 bricks will require 3J hours of the time of one mason, 10 man hours for helpers and laborers, 2 barrels of cement, 0.6 cubic yard of sand, and about 10 feet board measure of center- ing. One thousand bricks will make about 2 cubic yards of brickwork. To the costs, as estimated on the basis of materials and labor, must be added about 15 per cent for overhead and an addi- tional amount for the contractor's profit. The number of bricks required in various size sewers is shown in Table 67. A mason can lay more bricks per hour in a large sewer than in a small one as there is a smaller percentage of face work, there is more room to work, and it is easier to lay the bricks radially. The number of bricks laid and the rate of progress on various jobs are shown in Table 68. FIG. 128. Segmental Block Sewer at Clinton, Iowa, CONCRETE SEWERS 188. Construction in Open Cut. In the construction of sewer pipe of cement and concrete one of two methods may be em- ployed; 1st, to manufacture the pipe in a plant at some distance CONSTRUCTION IN OPEN CUT 313 from the place of final use, or 2nd, to manufacture the pipe in place. The methods of the manufacture of cement and concrete pipe which are to be transported to the place of use are treated in Chapter VIII. The process of constructing the pipes in place is ordinarily used for pipes 48 inches or more in diameter. For smaller sizes, brick, vitrified clay, and precast cement pipes are usually more economical. TABLE 66 ORGANIZATIONS FOR THE CONSTRUCTION OF BRICK AND BLOCK SEWERS Type of Work General Ratio on Basis of Four Brick Layers 15-foot, 5-ring Brick, Chicago 66-inch Circular Brick, Gary 84-inch Circular Brick, Gary 84- to 108-inch Sewer Brick in Detroit Tunnel 42-inch Lock- Joint Tile Block Foreman 1 1 1 1 1 1 Brick layers .... 4 12 6 6 5 2 Helpers 2 11 3 3 1 Scaffold men .... 2 21 3 Brick tossers .... 2 7 15 2 Brick carriers . . . 2 2 2 Cement mixers . . 2 6 6 5 1 Cement carriers . 2 10 8 Form setters .... 1 3 3 Laborers 1 8 19 3 14 7 Source of Information 1 Municipal Engineering, Vol.54,p.228 H. P. Gillette, Handbook of Cost Data The preparation of the foundation of a concrete sewer is similar to that for a brick sewer. If the ground is suitable the trench is shaped to the outside form of the sewer and the con- crete poured directly on it. In soft material which would give poor support to a sewer with a rounded exterior, the bottom of the trench is cut horizontal and a concrete cradle of poorer quality than that in the finished sewer is poured on the soft ground, on a board platform, on piles, or on cribbing supported on piles. -If the invert of the sewer is so flat that the concrete will stand without an inside form the shape of the invert is obtained 316 CONSTRUCTION by a screed or straight-edge which is passed over the surface of the concrete and guided on two centers, or on one center and the face of the finished work. The construction of a flat invert sewer at Baltimore is shown in Fig. 1. The center for the con- crete is shown in the foreground. When the concrete for the next section is poured it will be smoothed to shape by a screed or straight-edge resting on the face of the finished concrete and the center. The center is shaped to conform to that of the finished concrete. It is firmly staked in position and acts as a bulk- head for the concrete as it is poured, as well as a guide for the screed. TABLE 67 BRICK MASONRY IN CIRCULAR SEWERS. CUBIC YARDS PER LINEAR FOOT (From H. P. Gillette) Diameter, Feet and Inches One Ring (4 Inches) Two Ring (9 Inches) Three Ring (13 1 Inches) 2 0.103 0.240 2 6 0.125 0.280 3 0.147 0.327 3 6 0.169 0.371 4 0.191 0.415 4 6 0.213 0.458 5 0.234 0.501 0.802 5 6 0.256 0.545 0.867 6 0.278 0.589 0.933 6 6 0.633 1.000 7 0.677 1.063 7 6 0.720 1.128 8 0.763 1.193 8 6 0.807 1.260 9 0.851 1.325 9 6 0.895 1.390 10 0.938 1.456 If inside forms are to be used they ape made as units in lengths of 12 or 16 feet for wooden forms, and 5 feet for steel forms. The inside form is supported by precast concrete blocks placed under it and which are concreted into the sewer. It is held in position by cleats nailed to the outside form, to the sheeting, or RATE OF PROGRESS 317 Q) MJ > * {H T5 S 3 o3 ^ o ^ ^5 1 ^ | 1 | | ^ ^J & 2 S S ^ G 'T ill ^1 43 O X M 3~ o O O W H S CO 1-^ ^ i i co" 1 1 i *^ ^ -5 ^3 s PJ J" 1 "^ 03 fl 55 ^ ^ 3 O .3 .8 -2 ^ ^ ^"^ -g o ~g "o "S "S "*^ "*"* "*"* rv* H s oj ^3 2j ^ *3 "3 ?S 3 S c o o w bb- b ooow I (5 2~ .2 1 11 1 CD W) 2C ' 3 b g -5 b : r ^ | a^ r ^ O P 02 O CO oo^o 00 J ^ <_> i " v O5 1C u If Lg" SCO O CO CO i 1-1 i-H ^^ :S c^ i-^ f3 ^ PH CO CO d 5 o3 H 1 -g 02 r; |l O5 C^ CO iO >O co o co ^ CO ;o ; ; ^ 1 & ^ ^ O 02 fl ^ d "o *" $Q g ; ; Og ^ 'SS fe ffl S ^ !S 8 : : 39 8 c OJ CO I QJ 02 .Q C3 S 7 O CO 00 (N CO rj< f-ino f-iOK> Ift *-'**-*-K>OIOK> 32 -S36 n: o 52 & 56 - 60 S 64 I 68 72 76 80 84 88 92 96 100 <&* ^ K CJ t \O tO O CU 9 IB u> vo f- r- CO CO 00 00 00 S8 Date of Construction FIG. 148. Diagram Showing Rate of Depreciation of Pipe Sewers. Eng. News, Vol. 71, p. 86. which when added together represented the state of depreciation of the sewer. These sums were plotted as ordinates and the corresponding ages of the sewer were plotted as abscissas. The various points were taken cumulatively, and where the bond of the brickwork was broken (given a value of 72) plus other defects gave a total of 164 the sewer was considered as valueless and not worth repair. The scale of 164 was later reduced to a percentage basis as shown on the right of the figure. Fig. 148 shows a similar diagram for the depreciation of pipe sewers. VALUATION OF SEWERS 351 It was concluded that the life of a brick sewer in New York is 64 years. Some of the sewers examined were over 200 years old. The total original cost of 483 miles of brick, pipe and wood sewers was figured as $23,880,000 with a present worth of $18,665,000 and an average annual depreciation of 2.2 per cent. In figuring these amounts no account was taken of obsolescence. The deterioration of catch-basins proceeded at about the same rate as for brick sewers. CHAPTER XIII COMPOSITION AND PROPERTIES OF SEWAGE 208. Physical Characteristics. Sewage is the spent water supply of a community containing the wastes from domestic, industrial, or commercial use, and such surface and ground water as may enter the sewer. 1 Sewages are classed as: domestic sewage, industrial waste, storm water, surface water, street wash, and ground water. Domestic sewage is the liquid dis- charged from residences or institutions and contains water closet, laundry, and kitchen wastes. It is sometimes called sani- tary sewage. Industrial sewage is the liquid waste resulting from processes employed in industrial establishments. Storm water is that part of the rainfall which runs over the surface of the ground during a storm and for such a short period following a storm as the flow exceeds the normal and ordinary run-off. Surface water is that part of the rainfall which runs over the surface of the ground some time after a storm. Street wash is the liquid flowing on or from the street surface. Ground water is water standing in or flowing through the ground below its surface. Ordinary fresh sewage is gray in color, somewhat of the appear- ance of soapy dish water. It contains particles of suspended matter which are visible to the naked eye. If the sewage is fresh the character of some of the suspended matter can be dis- tinguished as: matches, bits of paper, fecal matter, rags, etc. The amount of suspended matter in sewage is small, so small as to have no practical effect on the specific gravity of the liquid nor to necessitate the modification of hydraulic formulas developed for application to the flow of water. The total suspended matter in a normal strong domestic sewage is about 500 parts per 1,000,000. It is represented graphically in Fig. 149. The quantity of organic or volatile suspended matter 1 Similar to definition proposed by the Am. Public Health Ass'n. 352 PHYSICAL CHARACTERISTICS 353 is about 200 parts per 1,000,000. It is shown graphically in the smaller cube in Fig. 149. The odor of fresh sewage is faint and not necessarily unpleasant. It has a slightly pungent odor, somewhat like a damp unven- tilated cellar. Occasionally the odor of gasoline, or some other predominating waste matter may hide all other odors. Stale sewage is black and gives off nauseating odors of hydrogen sulphide and other gases. If the sewage is so stale as to become septic, bubbles of gas will be seen breaking the sur- face and a black or gray scum may be present. Before the South Branch of the Chicago River was cleaned up and flushed this scum became so thick in places, particularly in that portion of the Stock Yards where the river became known as Bubbly Creek, that it is said that weeds and small bushes "sprouted in it, and chickens and small animals ran across its surface. A physical analysis of sewage should include an observation of its appearance, and a determination of its temperature, tur- bidity, color, and odor, both hot and cold. The temperature is useful in indicating certain of the antecedents of the sewage, its effect on certain forms of bacterial life, and its effect on the possible content of dissolved gases. Temperatures higher than normal are indicative of the presence of trades wastes discharged while hot into the sewers. A low temperature may indicate the presence of ground water. If the temperature is much over 40 C. bacterial action will be inhibited and the content of dis- solved gases will be reduced. Turbidity, color, and odor deter- minations may be of value in the control of treatment devices, or to indicate the presence of certain trades wastes, which give typical reactions. Since all normal sewages are high in color and turbidity, the relative amounts of these two constituents FIG. 149. Graphical Representation of Relative Volumes of Liquids and Solids in Sewage. 354 COMPOSITION AND PROPERTIES OF SEWAGE in two different sewages has little significance regarding the relative strengths of the two .sewages or the proper method of treating them. A fresh domestic sewage should have no highly offensive odor. The presence of certain trades wastes can be detected sometimes in fresh sewages, and a stale sewage may sometimes be recognized by its odor. Sewage is a liability to the community producing it. Although some substances of value can be obtained from sewage l the cost of the processes usually exceed the value of the substances obtained. Where it becomes necessary to treat sewage the value of these substances may be helpful in defraying the cost of treatment. 209. Chemical Composition. Sewage is composed of mineral and organic compounds which are either in solution or are sus- pended in water. In making a standard chemical analysis of sewage only those chemical radicals and elements are determined which are indicative of certain important constituents. Neither a complete qualitative nor quantitative analysis is made. A sewage analysis will not show, therefore, the number of grams of sodium chloride present or any other constituent. A complete standard sanitary chemical analysis will report the constituents as named in the first column of Table 71. The quantities of these materials found in average strong, medium and weak sewages are also shown in this table. These values are not intended as fixed boundaries between sewages of different strengths. They are presented merely as a guide to the inter- pretation of sewage analyses. The principal objects of a chemical analysis of sewage are to determine its strength and its state of decomposition. The influents and effluents of a sewage treatment device are analyzed to aid in the control of the device and to gain information con- cerning the effect of the treatment. Chemical and other analyses, in connection with the desired conditions after disposal, will indicate the extent of treatment which may be required. The standard methods of water and sewage analysis adopted by the American Public Health Association have been generally accepted by sanitarians. These uniform methods make possible com- 1 Economic Values in Sewage and Sewage Sludge, by Raymond Wells, Proceedings Am. Society Municipal Improvements, Nov. 12, 1919. Eng. News-Record, Vol. 83, 1919, p. 948. CHEMICAL COMPOSITION 355 3 Is r^ fli II |l | fS'a S 'o W OH i 2 ~ < .2 3 02 Q bC eo O O O o 2 a- O t5i ffl S I O5 C^ oo oo p p co oo CO O i i CO OOiOiOO'-iCO O I-H O O I-H I-H iOO5O5OO^O 10 COOt^-COiOCS O5 O CM coodco I-H 1C ICI-H CO C5 O FH ; sr ^ cc O *^^ C S I III 1 : "I S -* : ^ 1 S : S C Zl **^ ^3 < t liili i 356 COMPOSITION AND PROPERTIES OF SEWAGE parisons of the results obtained by laboratories working according to these standards. 210. Significance of Chemical Constituents. Organic nitro- gen and free ammonia taken together are an index of the organic matter in the sewage. Organic nitrogen includes all of the nitrogen present with the exception of that in the form of ammonia, nitrites, and nitrates. Free ammonia or ammonia nitrogen is the result of bacterial decomposition of organic matter. A fresh cold sewage should be relatively high in organic nitrogen and low in free ammonia. A stale warm sewage should be relatively high in free ammonia and low in organic nitrogen. The sum of the two should be unchanged in the same sewage. Nitrites (RN02) and nitrates (RNOs) 1 are found in fresh sewages only in concentrations of less than one part per million. In well-oxidized effluents from treatment plants the concen- tration will probably be much higher. Nitrates contain one more atom of oxygen than nitrites. They represent the most stable form of nitrogenous matter in sewage. Nitrites are not stable and are reduced to ammonias or are oxidized to nitrates. Their presence indicates a process of change. They are not found in large quantities in raw sewage because their formation requires oxygen which must be absorbed from some other source than the sewage. In an ordinary sewer or sluggishly flowing open stream this absorption cannot take place from the atmosphere with sufficient rapidity to supply the necessary oxygen. Oxygen consumed is an index of the amount of carbonaceous matter readily oxidizable by potassium permanganate. It does not indicate the total quantity of any particular constituent, but it is the most useful index of carbonaceous matter. Car- bonaceous matter is usually difficult of treatment and a high oxygen consumed is indicative of a sewage difficult to care for. The amount of oxygen consumed, as expressed in the analysis, is dependent on the amount of oxidizable carbonaceous matter present, the oxidizing agent used, and the time and temperature of contact of the sewage and the oxidizing agent. It is essential therefore that the test be conducted according to some standard method, since the results are of value only as compared with results obtained under similar conditions. Total solids (residue on evaporation) are an index of the 1 R represents any chemical element such as K, Na, etc. SIGNIFICANCE OF CHEMICAL CONSTITUENTS 357 strength of the sewage. They are made up of organic and inorganic substances. The inorganic substances include sand, clay, and oxides of iron and aluminum, which are usually insolu- ble, and chlorides, carbonates, sulphates and phosphates, which are usually soluble. The insoluble inorganic substances are undesirable in sewage because of their sediment forming prop- erties which result in the clogging of sewers, treatment plants, pumps, and stream beds. The soluble inorganic substances are generally harmless and cause no nuisance, except that the presence of sulphur may permit the formation of hydrogen sulphide, which has a highly offensive odor. The organic sub- stances are: carbo-hydrates, fats, and soaps, which are car- bonaceous and are difficult of removal by biological processes; and the nitrogenous substances such as urea, proteins, amines, and amino acids. The inorganic and organic substances may be either in solution or suspension or in a colloidal condition. Volatile solids are used as an index of the organic matter present, as it is assumed that the organic matter is more easily volatilized than the inorganic matter. The amount of volatile inorganic matter present is usually so small as to be negligible. Fixed solids are reported as the difference between the total and volatile solids. They are therefore representative of the amount of inorganic matter present. Suspended matter is the undissolved portion of the total solids. High volatile suspended matter is an indication of offensive qualities in the nature of putrefying organic matter, whereas fixed suspended matter is indicative of inoffensive inorganic matter. It is difficult to obtain a sample of sewage which will represent the amount of suspended matter in the sewage, since a sample taken from near the surface will contain less inorganic matter and grit than a sample taken near the bottom. Settling solids are indicative of the sludge forming properties of the sewage and of the probable degree of success of treatment by plain sedimentation. Volatile settling solids indicate the property of the formation of offensive putrefying sludge banks. There is no chemical test which will indicate the scum-forming properties of sewage. Fixed settling solids indicate the presence of inorganic matter, probably gritty material such as sand, clay, iron oxide, etc. Colloidal matter is material which is too finely divided to be 358 COMPOSITION AND PROPERTIES OF SEWAGE removed by filtration or sedimentation, yet is not held in solu- tion. It can sometimes be removed by violent agitation in the presence of a flocculent precipitate, as in the treatment with activated sludge, or by the flocculent precipitate alone, as in chemical precipitation, or by the acidulation of the sewage so as to precipitate the colloids. Colloidal matter is probably the result of the constant abrasion of finely divided suspended matter while flowing through the sewer or other channel. High colloidal matter may therefore indicate a stale sewage, or the presence of a particular trades waste. Colloids are difficult of removal. For this reason, where sewage is to be treated, turbulence in the tributary channels should be avoided. Alkalinity may indicate the possibility of success of the biologic treatment of sewage, since bacterial life flourishes better in a slightly alkaline than in a slightly acid sewage. Within the normal limits of the amount of alkalinity in sewage the exact amount has little significance in sewage analyses. Sewages are normally slightly alkaline. An abnormal alkalinity or acidity may indicate the presence of certain trades wastes necessitating special methods of treatment. A method of sewage treatment may be successful without changing the amount of alkalinity in the sewage since the amount of alkalinity is not inherently an objection. Chlorine, in the form of sodium chloride, is an inorganic sub- stance found in the urine of man and animals. The amount of chlorine above the normal chlorine content of pure waters in the district is used as an index of the strength of the sewage. The chlorine content may be affected by certain trades wastes such as ice-cream factories, meat-salting plants, etc., which will increase the amount of chlorine materially. Since chlorine is an inorganic substance which is in solution it is not affected by biological processes nor sedimentation. Its diminution in a treatment plant or in a flowing stream is indicative of dilution and the reduction of chlorine will be approximately proportional to the amount of dilution. Fats have a recoverable market value when present in sufficient quantity to be skimmed off the surface of the sewage. Ordinarily fats are an undesirable constituent of sewage as they precipitate on and clog the interstices in filtering material, they form objectionable scum in tanks and streams, and they are acted SIGNIFICANCE OF CHEMICAL CONSTITUENTS 359 on very slowly by biological processes of sewage treatment. Although fats are carbonaceous matter they are not indicated by the oxygen consumed test because they are not easily oxidized. They are therefore determined in another manner; by evapora- tion of the liquid and extracting the fats from the residue by dissolving them in ether. Relative stability and bio-chemical oxygen demand are the most important tests indicating the putrefying character- istics of sewage. Since stability and putrescibility have opposite meanings the relative stability test is sometimes called the putrescibility test. The relative stability of a sewage is an expression for the amount of oxygen present in terms of the amount required for complete stability. A relative stability of 75 signifies that the sample examined contains a supply of available oxygen equal to 75 per cent of the amount of oxygen which it requires in order to become perfectly stable. The available oxygen is approximately equivalent to the dissolved oxygen plus the available oxygen of nitrate and nitrite. 1 TABLE 72 RELATIVE STABILITY NUMBERS Time Required for Decolorization at 20 C. Days Relative Stability Number Time Required for Decoloriza- tion at 20 C. Days Relative Stability Number 0.5 11 8.0 84 1.0 21 9.0 87 1.5 30 10.0 90 2.0 37 11.0 92 2.5 44 12.0 94 3.0 50 13.0 95 4.0* 60 14.0 96 5.0 68 16.0 97 6.0 75 18.0 98 7.0 80 20.0 99 * Routine tests are ordinarily incubated for this period only, and if not decolorized in this time are recorded as stable. Standard Methods of Water Analysis, American Public Health Asso- ciation, 1920. 360 COMPOSITION AND PROPERTIES OF SEWAGE The relative stability numbers, given in Table 72, are computed from the expression, S = 100(1 -0.7940 in which S is the stability number and t is the time in days that the sample has been incubated at 20 C. The bio-chemical oxygen demand is more directly an index of the consumption of available oxygen by the biological and chemical changes which take place in the decomposition of sewage or polluted water. As such it is a more valuable, though less easily performed test than the test of relative stability. The methods for the determination of the relative stability and the bio-chemical oxygen demand are given to show more clearly what these tests represent. The procedure in the relative stability test is to add 0.4 c.c. of a standard solution of methylene blue to 150 c.c. of the sample. The mixture is then allowed to stand in a completely filled and tightly stoppered bottle at 20 C. for 20 days or until the blue fades out due to the ex- haustion of the available oxygen. There are three methods in use for the determination of the biochemical oxygen demand; 1 the relative stability method, the excess nitrate method, and the excess oxygen method In the relative stability method the sample to be treated should have a relative stability of at least 50. If it is lower than this the sample should be diluted with water containing oxygen until the relative stability has been raised to or above this point. The oxygen demand in parts per million is then expressed as 0' = RP in which 0' is the oxygen demand, is the initial oxygen in parts per million (p. p.m.) in the diluting water or sewage, P is the proportion of sewage in the mixture expressed as a ratio, and R is the relative stability of the mixture expressed as a decimal. For the effluents from sewage treatment plants, polluted waters, and similar liquids, the total available oxygen expressed as the sum of the dissolved oxygen, nitrites, and nitrates, divided by 1 Determination of the Biochemical Oxygen Demand of Sewage and Industrial Wastes, by E. J. Theriault, Report of the U. S. Public Health Service, Vol. 35, May 7, 1920, No. 19, p. 1087. 2 Standard Methods of Water Analysis, American Public Health Asso- ciation, 1920. SIGNIFICANCE OF CHEMICAL CONSTITUENTS 361 the relative stability expressed as a decimal will give the bio- chemical oxygen demand. The excess nitrate method requires the determination of the total oxygen available as dissolved oxygen, nitrites, and nitrates and the addition of a sufficient amount of oxygen in the form of sodium nitrate to prevent the exhaustion of oxygen during a 10-day period of incubation. At the end of the period the total available oxygen is again deter- mined. The difference between the original and the final oxygen content represents the bio-chemical oxygen demand. The excess oxygen test requires the determination of the total avail- able oxygen as before, and the addition of a sufficient amount of oxygen, in the form of dissolved oxygen in the diluting water, to prevent exhaustion of the oxygen in a 10-day period of incu- bation. The difference between the original and final oxygen content represents the bio-chemical oxygen demand. Theriault concludes as a result of his tests, that the relative stability and excess nitrate methods are open to objections but that the excess oxygen method yields very accurate and consistent results with as little or less labor than is required by other methods. Dissolved oxygen represents what its name implies, the amount of oxygen (0%) which is dissolved in the liquid. Normal sewage contains no dissolved oxygen unless it is unusually fresh. It is well, if possible, to treat a sewage before the original dis- solved oxygen has been exhausted. Normal pure surface water contains all of the oxygen which it is capable of dissolving, as shown in Table 73. The presence of a smaller amount of oxygen than is shown in this table indicates the presence of organic matter in the process of oxidation, which may be in such quanti- ties as ultimately to reduce the oxygen content to zero. Normal pure ground waters may be deficient in dissolved oxygen because of the absence of available oxygen for solution. The presence of certain oxygen-producing organisms in polluted or otherwise potable surface waters may cause a supersaturation with oxygen however. The dissolved-oxygen test for polluted water is probably the most significant of all tests. If dissolved oxygen is found in a polluted water it means that putrefactive odors will not occur, since putrefaction cannot begin in the presence of oxygen. It is possible for different strata in a body of water to have different quantities of dissolved oxygen, and putrefaction may be proceeding 362 COMPOSITION AND PROPERTIES OF SEWAGE in the lower strata before the oxygen is exhausted from the upper strata. The oxygen content of a river water will indicate the ability of the river to receive sewage without resulting in a nuisance. TABLE 73 SOLUBILITY OF OXYGEN IN WATER Under an atmospheric pressure of 760 mm. of mercury, the atmosphere containing 20.9 per cent of oxygen. Temperature, degrees C 0.00 1 2 3 4 5 6 7 Oxygen in parts per million . . . 14.62 14.23 13.84 13.48 13.13 12.80 12.48 12.17 Temperature, degrees C 8 9 10 11 12 13 14 15 Oxygen in parts per million. . . 11.87 11.59 11.33 11.08 10.83 10.60 10.37 10.15 Temperature, degrees C 16 17 18 19 20 21 22 23 Oxygen in parts per million. . . 9.95 9.74 9.54 9.35 9.17 8.99 8.83 8.68 Temperature degrees C 24 25 26 27 28 29 30 Oxygen in parts per million. . . 8.53 8.38 8.22 8.07 7.92 7.77 7.63 211. Sewage Bacteria. A slight knowledge of the nature of bacteria is necessary in order that the biological changes which occur in the treatment of sewage may be understood. Bacteria are living organisms which are so small that it is difficult or impossible to study them either with the eye alone or with the aid of powerful microscopes. They are studied by means of cultures, stains, and certain characteristic phenomena such as the production of a gas, the production of a red colony on litmus lactose agar, etc. Bacteria occur in three forms: spherical, called coccus; cylindrical, called bacillus; and spiral, called spirillum. In size they vary from the largest at about 1/10,000 of an inch to sizes so small as to be invisible under the most powerful microscope. An ordinary size is 1/25,000 of an inch. The cylindrical or rod bacteria are about four times as long as they are wide. Some bacteria possess the power of motion due to the presence of flagella or hairs which can be moved and ORGANIC LIFE IN SEWAGE 363 cause the cell to progress at a rate as high as 18 cm. per hour, but usually the rate is very much less than this. The compo- sition of the bacterial cell has never been definitely determined. Bacteria are unicellular plants. They possess no digestive organs and apparently obtain their food by absorption from the surrounding media. Reproduction is by the division of the cell into two approximately equal portions. This reproduction may occur as frequently as once every half hour and if unchecked would quickly mount to unimaginable numbers. The natural cause limiting the growth of bacteria is the generation by the bacterium of certain substances such as the amino acids, which are injurious to cell life. The exhaustion of the food supply is not considered as an important cause of inhibition of multipli- cation. The products of growth of one species of bacteria may be helpful or harmful to other forms. Where the products are helpful the effect is known as symbiosis, and where harmful the effect is known as antibiosis. In sewage the presence of both aerobic and anaerobic bacteria is usually mutually helpful and the condition is an example of symbiosis. The aerobes, some- times called obligatory aerobes, are bacteria which demand available oxygen for their growth. The anaerobes, or obligatory anaerobes, can grow only in the absence of oxygen. There are other forms that are known as facultative anaerobes (or aerobes) whose growth is independent of the presence or absence of oxygen. Spores are formed by some bacteria when they are subjected to an unfavorable environment such as high temperatures, the absence of food, the absence of moisture, etc. Spores are cells in which growth and animation are suspended but the life of the cell is carried on through the unsuitable period, somewhat similar to the condition in a plant seed. 212. Organic Life in Sewage. Living organisms, both plants and animals, exist in sewage. Bacteria are the smallest of these organisms. Others, which can be studied easily under the microscope or can be seen with difficulty by the naked eye but which do not require special cultures for their study, are classed as microscopic organisms or plankton. Organisms which are large enough to be studied without the aid of a microscope or special cultures are classed as macroscopic. The part taken in the biolysis of sewage by macroscopic organisms belonging to 364 COMPOSITION AND PROPERTIES OF SEWAGE the animal kingdom, such as birds, fish, insects, rodents, etc., which feed upon substances in the sewage is so inconsequential as to be of no importance. Both plants and animals are found among the macroscopic organisms. Organisms in sewage may be either harmful, harmless, or beneficial. From the viewpoint of mankind the harmful organ- isms are the pathogenic bacteria. Their condition of life in sewage is not normal and in general their existence therein is of short duration. It may be of sufficient length, however, to permit the transmission of disease. The diseases which can be trans- mitted by sewage are only those that are contracted through the alimentary canal, such as typhoid fever, dysentery, cholera, etc. Diseases are not commonly contracted by contact of sewage with the skin nor by breathing the air of sewers. It is safe to work in and around sewage so long as the sewage is kept out of the mouth, and asphyxiating or toxic gases are avoided. The beneficial organisms in sewage are those on which dependence is placed for the success of certain methods of treat- ment. These organisms have not all been isolated or identified. The total number of bacteria in a sample of sewage has little or no significance. In a normal sewage the . number may be between 2,000,000 and 20,000,000 per c.c. and because of the extreme rapidity of multiplication of bacteria a sample showing a count of 1,000,000 per c.c. on the first analysis may show 4 to 5 times as many 3 or 4 hours later. A bacterial analysis of sewage is ordinarily of little or no value, since pathogenic organ- isms are practically certain to be present, there is no interest in the harmless organisms, and the helpful nitrifying and aerobic bacteria will not grow on ordinary laboratory media. Occa- sionally the presence of certain bacteria may indicate the presence of certain trades wastes. In general, the total bacterial count, as sometimes reported, represents only the number of bacteria which have grown under the conditions provided. It bears no relation to the total number of bacteria in the sample. The presence of bacteria in sewage is of great importance however, as practically all methods of treatment depend on bacterial action, and all sewages which do not contain deleterious trades wastes, contain or will support the necessary bacteria for their successful treatment, if properly developed. DECOMPOSITION OF SEWAGE 365 213. Decomposition of Sewage. If a glass container be filled with sewage and allowed to stand, open to the air, a black sedi- ment will appear after a short time, a greasy scum may rise to the surface, and offensive odors will be given off. This con- dition will persist for several weeks, after which the liquid will be- come clear and odorless. The sewage has been decomposed and is now in a stable condition. The decomposition of sewage is brought about by bacterial action the exact nature of which is uncertain. It 1 is well established that many of the chemical effects wrought by bacteria, as by other living cells, are due, not to the direct action of the protoplasm, but to the intervention of soluble ferments or enzymes. Enzymes are soluble ferments produced by the growth of the bacterial cell. In 2 many cases the enzymes diffuse out from the cell and exert their effort on the ambient substances . . . in others the enzyme action occurs within the cell and the products pass out, (for example) . . . the alcohol- producing enzymes of the yeast cell act upon sugar within the cell, the resulting alcohol and carbon dioxide being ejected. Other chemical effects may be brought about by the direct action of the living cells, but this has never been well established. Metabolism is the life process of living cells by which they absorb their food and convert it into energy and other products. It is the metabolism of bacterial growth that in itself or by the production of enzymes hastens the putrefactive or oxidizing stages of the organic cycles in sewage treatment. Bacteria can assimilate only liquid food since they have no digestive tract through which solid food can enter. The surrounding solids are dissolved by the action of the enzymes, the resulting solution diffusing through the chromatin or outer skin, and being digested throughout the interior cytoplasm. Bacteria are sometimes classified as parasites and saprophytes. The parasites live only on the growing cells of other plant or animal life. The saprophytes obtain their food only from the 1 Jordan, General Bacteriology, 1909, p. 91. 2 Ibid. 366 COMPOSITION AND PROPERTIES OF SEWAGE life products of living organisms and do not exist at the expense of the organisms themselves. Facultative saprophytes (or parasites) may exist on either living or dead tissue. The decomposition of sewage may be divided into anaerobic and aerobic stages. These conditions are usually, but not always, distinctly separate. The growth of certain forms of bacteria is concurrent, while the growth of other forms is dependent on the results of the life processes of other bacteria in the early stages of decomposition. When sewage is very fresh it contains some oxygen. This oxygen is quickly exhausted so that the first important step in the decomposition of sewage is carried on under anaerobic condi- tions. This is accompanied by the creation of foul odors of organic substances, ammonia, hydrogen sulphide, etc.; other odorless gases such as carbon dioxide, hydrogen, and marsh gas, the latter being inflammable and explosive; and other com- plicated compounds. An exception to the rule that putrefac- tion takes place only in the absence of oxygen is the production of other foul-smelling substances by the putrefactive activity of obligatory and facultative aerobes. Hydrogen sulphide may be produced apparently in the presence of oxygen the action which takes place not being thoroughly understood. The biolysis of sewage is the term applied to the changes through which its organic constituents pass due to the metab- olism of bacterial life. Organic matter is composed almost exclusively of the four elements: carbon, oxygen, hydrogen, and nitrogen (COHN) and sometimes in addition sulphur and phosphorus. The organic constituents of sewage can be divided into the proteins, carbohydrates, and fats. The proteins are principally constituents of animal tissue, but they are also found in the seeds of plants. The principal distinguishing character- istic of the proteins is the possession of between 15 and 16 per cent of nitrogen. To this group belong the albumens and casein. The carbohydrates are organic compounds in which the ratio of hydrogen to oxygen is the same as in water, and the number of carbon atoms is 6 or a multiple of 6. To this group belong the sugars, starches and celluloses. The fats are salts formed, together with water, by the combination of the fatty acids with the tri-acid base glycerol. The more common fats are stearin, palmatin, olein, and butyrine. The soaps are mineral salts of the THE NITROGEN CYCLE 367 fatty acids formed by replacing the weak base glycerol with some of the stronger alkalies. The first state in the biolysis of sewage is marked by the rapid disappearance of the available oxygen present in the water mixed with organic matter to form sewage. In this state the urea, ammonia, and other products of digestive or putrefactive decomposition are partially oxidized and in this oxidation the available oxygen present is rapidly consumed, the conditions in the sewage becoming anaerobic. The second state is putre- faction in which the action is under anaerobic conditions. The proteins are broken down to form urea, ammonia, the foul- smelling mercaptans, hydrogen sulphide, etc., and fatty and aromatic acids. The carbohydrates are broken down into their original fatty acid, water, carbon dioxide, hydrogen, methane, and other substances. Cellulose is also broken down but much more slowly. The fats and soaps are affected somewhat similarly to the hydrocarbons and are broken down to form the original acids of their make up together with carbon dioxide, hydrogen, methane, etc. The bacterial action on facts and soaps is much slower than on the proteins, and the active biological agents in the biolysis of the hydrocarbons, fats, and soaps are not so closely confined to anaerobes as in the biolysis of the proteins. The third state in the biolysis of sewage is the oxidation or nitrification of the products of decomposition resulting from the putrefactive state. The products of decomposition are converted to nitrites and nitrates, which are in a stable condition and are available for plant food. It must be understood that the various states may be coexistent but that the conditions of the different states predominate approximately in the order stated. In the biolysis of sewage there is no destruction of matter. The same elements exist in the same amount as at the start of the biolytic action. 214. The Nitrogen Cycle. Nitrogen is an element that is found in all organic compounds. Its presence is necessary to all plant and animal life. The nitrogenous compounds are most readily attacked by bacterial action in sewage treatment. The non-nitrogenous substances such as soaps and fats, and the inor- ganic compounds are more slowly affected by bacterial action alone. The element nitrogen passes through a course of events from life to death and back to life again that is known as the 368 COMPOSITION AND PROPERTIES OF SEWAGE Nitrogen Cycle. It is typical of the cycles through which all of the organic elements pass. Upon the death of a plant or animal, decomposition sets in accompanied by the formation of urea which is broken down into ammonia. This is known as the putrefactive stage of the Nitrogen Cycle. The next state is nitrification in which the compounds of ammonia are oxidized to nitrites and nitrates, and are thus prepared for plant food. In the state of plant life the nitrites and nitrates are denitrified so as to be available as a plant or animal food. The highest state of the Nitrogen Cycle is animal life, in which nitrogen is a part of the living animal substance or is charged from protein to urea, ammonia, etc., by the functions of life in the animal. Upon the death of this animal organism the cycle is repeated. The Nitrogen Cycle, like the cycle of Life and Death, is purely an ideal condition as in nature there are many short circuits and back currents which prevent the continuous progression of the cycle. The con- ception of this cycle is an aid, however, in understanding the processes of sewage treatment. 215. Plankton and Macroscopic Organisms. In general the part played by these organisms in the biolysis of sewage is not sufficiently well understood to aid in the selection of methods of sewage treatment involving their activities. The presence in bodies of water receiving sewage, of certain plankton which are known to exist only when putrefaction is not imminent, indicates that the body of water into which the discharge of sewage is occurring is not being overtaxed. The control of sewage treatment plant effluents so as to avoid the poisoning of fish life .or the contamination of shell fish is likewise important. The study of plankton and macroscopic life in the treatment of sewage is an open field for research. 216. Variations in the Quality of Sewage. The quality of sewage varies with the hour of the day and the season of the year. Some of the causes of these variations are: changes in the amount of diluting water due to the inflow of storm water or flushing of the streets or sewers; variations in domestic activities such as the suspension of contributions of organic wastes during the night, Monday's wash, etc.; characteristics of different industries which discharge different kinds of wastes according to the stage of the manufacturing process, etc. In general VARIATIONS IN THE QUALITY OF SEWAGE 369 ! TABLE 74 SEWAGE ANALYSES SHOWING HOURLY, DAILY, AND SEASONAL VARIATIONS IN QUALITY Place Time Total Nitro- gen Chlo- rine Sus- pended Matter Remarks Refer- ence Marion Ohio . Mid't-noon, 5-21-06. 45 53 190 Industrial 1 Noon-mid't 5-21-06. 37 94 133 Domestic 1 Westerville, Ohio Day 10.2 76 118 f college 1 Night 2.6 74 41 \ town 1 Columbus, Ohio 1904-1905 Mid't to 2 a.m. 4.6 50 131 2 2 a.m. to 4 a.m. 3.0 52 95 2 4 a.m. to 6 a.m. 2.3 51 83 2 6 a.m. to 8 a.m. 2.7 48 83 2 8 a.m. to 10 a.m. 16.3 66 476 2 10 a.m. to noon 11.4 100 324 2 Noon to 2 p.m. 11.3 86 246 2 2 p.m. to 4 p.m. 12.3 78 246 2 4 p.m. to 6 p.m. 22.0 78 368 2 6 p.m. to 8 p.m. 8.2 71 209 2 8 p.m. to 10 p.m. 7.8 80 120 2 10 p.m. to mid't 6.2 56 117 2 Center Ave., Chicago. Mid't to 3 a.m. 123 3 4 a.m. to 7 a.m. 316 3 8 a.m. to 11 a.m. 608 3 Noon to 3 p.m. 785 3 4 p.m. to 7 p.m. 717 3 8 p.m. to 11 p.m. 287 3 Columbus, Ohio Sunday 6.7 55 858 2 Monday 9.1 66 1048 2 Tuesday 9.4 69 1024 2 Wednesday 9.6 68 1005 2 Thursday 9.2 66 990 2 Friday 9.2 67 1018 2 Saturday 9.3 67 1016 2 Baltimore, 1907-1908. Aug. 1 to Sept. 1 16.0 246 4 Sept. 4 to Oct. 3 19.0 190 4 Oct. 6 to Nov. 4 20.0 188 4 Nov. 15 to Nov. 29 20.0 164 4 Dec. 3 to Dec. 29 20.0 123 4 Jan. 6 to Jan. 21 19.0 127 4 Feb. 2 to Feb. 26 20.0 149 4 Feb. 29 to Mar. 24 28.0 274 4 Mar. 27 to April 29 25.0 165 4 April 30 to May 26 19.0 104 4 June 8 to July 11 15.0 88 4 July 13 to Aug. 8 9.5 124 4 References: 1. 1908 Report of the Ohio State Board of Health. 2. Report on Sewage Purification at Columbus, Ohio, by G. A. Johnson, 1905. 3. Report on Industrial Wastes from the Stock Yards and Packingtown in Chicago, by the Sanitary District of Chicago. 1921. 4. Report of the Baltimore Sewerage Commission, 1911. 370 COMPOSITION AND PROPERTIES OF SEWAGE night sewage is markedly weaker than day sewage in both domestic and industrial wastes, but in specific cases the varying strength depends entirely upon the characteristics of the district. Some analyses are given in Table 74, which emphasize these points. 217. Sewage Disposal. Previous to the development of the water-carriage method for removing human excreta and other liquid wastes the solid matter was disposed of by burial and the liquid wastes were allowed to seep into the ground or to run away over its surface. Following the development of the water- carriage system, which necessitated the development of sewers, the problem of ultimate disposal was rendered more serious by the concentration of human excreta together with a large volume of water. The unthinking citizen believes the problem of sewage disposal is solved when the toilet is flushed or the bath tub is drained. The problem may more truly be said to commence at this point. It would appear that the simplest method of disposal of sewage would be to discharge it into the nearest water course. Unfortunately the nature of sewage is such that it may be either highly offensive to the senses or dangerous to health or both, when discharged in this manner. Only the most fortunate communities are favored with a body of water of sufficient size to receive sewage without creating a nuisance. The problems of sewage disposal are to prevent nuisances causing offense to sight and smell; to prevent the clogging of channels; to protect pumping machinery; to protect public water supplies; to protect fish life; to prevent the contamination of shell fish; to recover valuable constituents of the sewage; to enrich and to irrigate the soil; to safeguard bathing and boat- ing ; for other minor purposes ; and in some cases to comply with the law. Sewage may be treated to attain one or more of these objects by methods of treatment varying as widely as the objects to be attained. 218. Methods of Sewage Treatment. In studying the sub- ject of sewage treatment it must be borne in mind that it is impossible to destroy any of the elements present. They may be removed from the mixture only by gasification, straining or sedimentation. Their chemical combinations may be so changed, however, as to result in different substances than those intro- METHODS OF SEWAGE TREATMENT 371 duced to the treatment plant. It is with these chemical changes that the student of sewage treatment is interested. The methods of sewage treatment can be classified as mechan- ical, chemical and biological. These classifications are not sepa- rated by rigid lines but may overlap in certain treatment devices or methods. Mechanical methods of treatment are exemplified by sedimentation, and screening. Chemical precipitation and sterilization are examples of chemical methods. The biological methods, the most important of all, include dilution, septiciza- tion, filtration, sewage farming, activated sludge, etc. If for any reason it is desired to treat sewage by more than one of these methods the procedure should follow as nearly as possible the order of the occurrence of the phenomena in the natural biolysis of sewage. For example, in one treatment plant the sewage would first pass through a grit chamber where the coarse sediment would be removed, then through a screen where the floating matter and coarse suspended matter would be removed, then to a sedimentation basin where some finer suspended matter might settle out, then to a digestive tank where the solid matter deposited would be worked upon by bacterial action and partially liquefied. Simultaneous to the liquefaction of the deposited solid matter the liquid effluent from the digestive tank might proceed to an aerating device to expedite oxidation, then to an aerobic filter, and finally to disposal by dilution. CHAPTER XIV DISPOSAL BY DILUTION 219. Definition. Disposal of sewage by dilution is the dis- charge of raw sewage or the effluent from a treatment plant into a body of water of sufficient size to prevent offense to the senses of sight and smell, and to avoid danger to the public health. 220. Conditions Required for Success. Among the desired conditions for successful disposal by dilution are: adequate currents to prevent sedimentation and to carry the sewage away from all habitations before putrefaction sets in, or sufficient diluting water high in dissolved oxygen to prevent putrefaction; a fresh or non-septic sewage; absence of floating or rapidly settling solids, grease or oil; and absence of back eddies or quiet pools favorable to sedimentation in the stream into which disposal is taking place. The conditions which should be pre- vented are: offensive odors due to sludge banks, the rise of septic gases, and unsightly floating or suspended matter. In some instances the pollution of the receiving body of water is undesirable and the sewage must be freed from pathogenic organisms and the danger of aftergrowths minimized before disposal. Such con- ditions are typified at Baltimore, where the sewage is discharged into Back Bay, an arm of Chesapeake Bay. One of the impor- tant industries of the state of Maryland is the cultivation of oysters. The pollution of the Bay was therefore so objectionable that care- ful treatment of the Baltimore sewage has been a necessary preliminary to final disposal by dilution. It is unwise to draw public water supplies, without treatment, from a stream receiving a sewage effluent, no matter how careful or thorough the treat- ment of the sewage. The treatment of the sewage is a safe- guard, and lightens the load on the water purification plant, but under no considerations can it be depended upon to protect the community consuming the diluted effluent. 372 SELF-PURIFICATION OF RUNNING STREAMS 373 The sewer outlet should be located well out in the current of the stream, lake, or harbor. Deeply submerged outlets are usually better than an outlet at the surface, as a better mixture of the sewage and water is obtained. The discharge of sewage into a body of water of which the surface level changes, alternately covering and exposing large areas of the bottom is unwise, as the ludge which is deposited during inundation will cause offensive odors when uncovered. Such conditions must be carefully guarded against when selecting a point of disposal in tidal estuaries because of the frequent fluctuations in level. 221. Self-Purification of Running Streams. The self-purifi- cation of running streams is due to dilution, sedimentation, and oxidation. The action is physical, chemical, and biological. When putrescible organic matter is discharged into water the offensive character of the organic matter is minimized by dilution. If the dilution is sufficiently great, it alone may be sufficient to prevent all nuisance. The oxidation of the organic matter commences immediately on its discharge into the diluting water due to the growth and activity of nitrifying and other oxidizing organisms and to a slight degree to direct chemical reaction. So long as there is sufficient oxygen present in the water septic conditions will not exist and offensive odors will be absent. When the organic matter is completely nitrified or oxidized there will be no further demand on the oxygen content of the stream and the stream will be said to have purified itself. At the same time that this oxidation is going on some of the organic matter will be settling due to the action of sedimentation. If oxidation is completed before the matter has settled on the bottom the result will be an inoffensive silting up of the river. If oxidation is not complete, however, the result will be offensive putrefying sludge banks which may send their stinks up through the superimposed layers of clean water to pollute the surrounding atmosphere. The most important condition for the successful self-purifi- cation of a stream is an initial quantity of dissolved oxygen to oxidize all of the organic matter contributed to it, or the addition of sufficient oxygen subsequent to the contribution of sewage to complete the oxidation. Oxygen may be added through the dilu- tion received from tributaries, through aeration over falls and rapids, or by quiescent absorption from the atmosphere. The 374 DISPOSAL BY DILUTION rapidity of self-purification is dependent on the character of the organic matter,, the presence of available oxygen, the rate of reaeration, temperature, sedimentation, and the velocity of the current. Sluggish streams are more likely to purify themselves in a shorter distance and rapidly flowing turbulent streams are more likely to purify themselves in a shorter time, other conditions being equal. Although the absorption of oxygen by a stream whose surface is broken is more rapid than through a smooth unbroken surface, the growth of algae, biological activity, the effect of sunlight, and sedimentation are more potent factors and have a greater effect in sluggish streams than the slightly more rapid absorption of oxygen in a turbulent stream. It is frequently more advantageous to discharge sewage into a swiftly moving stream, however, regardless of the conditions of self -purification, as the undesirable conditions which may result occur far from the point of disposal and may be offensive to no one. The sewage from a population of about 3,000,000 persons residing in and about Chicago is discharged into the Chicago Drainage Canal. It ultimately reaches tide water through the Des Plaines, the Illinois, and the Mississippi Rivers. The action occurring in these channels is one of the best illustrations known of the self-purification of a stream. In Table 75 are shown the results of analyses of samples taken at various points below the mouth of the Chicago River where the diluting water from Lake Michigan enters, to Graf ton, Illinois, at the junction of the Illinois and Mississippi Rivers about 40 miles above St. Louis. The effect of the physical characteristics of the stream on its chemical composition is well illustrated in this table. The rise in the chlorine content between Lake Michigan and the entrance to the Drainage Canal is a measure of the addition of sewage. Since the chlorine is an inorganic substance which is not affected by biologic action, its loss in concentration in the lower reaches of the rivers is due to dilution by tributaries and sedimentation, e.g., between the end of the canal at Lockport and the sampling point at Joliet, the entrance of the Des Plaines River reduces the concentration of chlorine from 124.5 to 41.5 parts per million. The entrance of the Kankakee River at Dresden Heights further reduces the chlorine to 24.5 p.p.m. The increase of albuminoid and ammonia nitrogen accompanied SELF-PURIFICATION OF RUNNING STREAMS 375 PQ K fl a.s .2^ S.e of g I! iga !l & .2 .s5 s a i.S.S - ' t-l t-> 888 PnpHpL, , rt< O CO iO ' i-i rH O ^ 00 t^ (M O "^ !>-OOOOiO -COCO |> ^5 *O CO OS t > * 00 * CO O rH i t rH CO "^ 'i-l O TJ -CO rH -O -O :g : :^J CO -tOiOlM -rH rt< iO O OS 00 O 00 O rj O CO OO COOCO O O CO O3 !> -CO -00 H -OS HJll Q 010 rt| 00 COCO O O CO O O OS >O rH iO 00 O V ww 8 9 ^ ^ p a ^g r fc iililjias^f :8S : : : % : ': : 1 Sis B : iiJl?i; i.allll 11 C fi 3^ 376 DISPOSAL BY DILUTION by a decrease in nitrites and nitrates, between the upper end of the canal at Bridgeport and its lower end at Lockport indicates the reducing action proceeding therein. The oxidizing action over the various dams and the effect of dilution with water containing oxygen is shown between miles 34 and 38, at mile 79, and at mile 294. The excellent effect of quiescent sedimentation and aeration in Peoria Lakes is shown between miles 145, 161 and 165. 222. Self-Purification of Lakes. Sewage may be disposed of into lakes with as great success as into running streams if condi- tions exist which are favorable to self -purification. Lakes and rivers purify themselves from the same causes; oxidation, sedi- mentation, etc., but in the former the currents are much less pronounced and may be entirely absent. In shallow lakes (20 feet or less in depth) dependence must be placed on horizontal currents and the stirring action of the wind to keep the water in motion in order that the sewage and the diluting water may be mixed. In deeper bodies of water, currents induced by the wind are helpful but entire dependence need not be placed upon them. Vertical currents, and the seasonal turnovers in the spring and fall completely mix the waters of the lake above those layers of water whose temperature never rises higher than 4 C. In the early winter the cold air cools the surface waters of a lake. The cooling increases the density of the surface water causing it to sink, and allowing the warmer layers below to rise and become cooled. After the temperature of the entire lake has reached 4 C. the vertical currents induced by temperature cease, as continued cooling decreases the density of the surface water maintaining the same layer at the surface. In the spring as the temperature of the surface water rises to 4 C. and above it becomes heavier and drops through the colder water below causing vertical currents. These phenomena are known as the fall and spring turnovers. The former is more pronounced. These turnovers are effective in assisting in the self-purification of lakes. 223. Dilution in Salt Water. The oxygen content in salt water is about 20 per cent less than in fresh water at the same temperature. The greater content of matter in solution in salt water reduces its capacity to absorb many sewage solids. This, together with the chemical reaction between the constitu- QUANTITY OF DILUTING WATER NEEDED -377 ents of the salt water and those of the sewage, serve to precipitate some of the sewage solids and to form offensive sludge banks. The evidence of the action which takes place in the absorption of oxygen from the atmosphere by salt water and its effect on dissolved sewage solids is conflicting, but in general fresh water is a better diluting medium than salt water. Black and Phelps have made valuable studies of the relative rates of absorption of oxygen from the air by fresh and salt water. The results of their experiments are published in a Report to the Board of Estimate and Apportionment of N. Y. City, made March 23, 191 1. 1 Concerning these rates they conclude: Therefore there is no reason to believe that the reaeration of salt water follows any other laws than those we have determined mathematically and experi- mentally for fresh water. In the absence of fuller infor- mation on the effect of increased viscosity upon the diffusion coefficient, it can only be stated that the rate of reaeration of salt water is less than that of fresh water, in proportion to the respective solubilities of oxygen in the two waters, and still less, but to an unknown extent, by reason of the greater viscosity and consequent small value of the diffusion coefficient. 224. Quantity of Diluting Water Needed. In a large majority of the problems of disposal of sewage by dilution it is not neces- sary to add sufficient diluting water to oxidize completely all organic matter present. Ordinarily it is sufficient to prevent putrefactive conditions until the flow of the stream, lake, or tidal current, has reached some large body of diluting water or where putrefaction is no longer a nuisance. It is never desirable to allow the oxygen content of a stream to be exhausted as putres- cible conditions will exist locally before exhaustion is complete. The exact point to which oxygen can be reduced in safety is in some dispute. Black and Phelps have assumed 70 per cent of saturation as the allowable limit; Fuller has placed it at 30 per cent; Kinnicutt, Winslow, and Pratt have placed it at 50 per cent. Since the reaction between the oxygen and the organic matter is quantitative, others have placed the limit in terms of parts per million of oxygen. Wisner, 2 has recommended a mini- 1 Reprinted in Vol. Ill of Contributions from the Sanitary Research Laboratory of Massachusetts Institute of Technology. 2 Formerly Chief Engineer of the Sanitary District of Chicago. 378 DISPOSAL BY DILUTION mum of 2.5 p.p.m. as the limit for the sustenance of fish life, which is not far from Fuller's limit for hot-weather conditions. Formulas of various types have been devised to express the rate of absorption of oxygen with a given quantity of diluting water which is mixed with a given quantity and quality of sewage. The quantity of sewage is sometimes expressed in terms of the tributary population or in other ways. Knowing the rate at which oxygen is exhausted and the velocity of flow of the stream, the point at which the oxygen will be reduced to the limit allowed is easily determined. The accuracy of none of these formulas has been proven, and their use, without an understanding of the effect of local conditions, may lead to error. They may be used as a check on the bio-chemical oxygen demand determinations, which should be conclusive. The following formula, based on the work of Black and Phelps, is a guide to the amount of sewage which can be added to a stream without causing a nuisance. It is: 0' log o~ in which C =per cent of sewage allowed in the water; O'=per cent of saturation or the p.p.m. of oxygen in the mixture at the time of dilution; 0=per cent of saturation or the p.p.m. of oxygen in the stream after period of flow to point beyond which no nuisance can be expected; =time in hours required for the stream to flow to this point; k = constant determined by test determinations of the factors in the following expression: k - " in which O'i =per cent of saturation or the p.p.m. of oxygen in the diluting water before mixing with the sewage; Oi=per cent of saturation or the p.p.m. of oxygen in an artificial mixture made in the laboratory, after t\ hours of incubation; QUANTITY OF DILUTING WATER NEEDED 379 d = per cent of sewage in the mixture; ti = number of hours of incubation of the mixture of sewage and diluting water under laboratory conditions. In the solution of these formulas it is desired to determine the permissible amount of sewage to discharge into a given quantity of diluting water. This value is expressed by C in the first equation. In solving this equation: 0' is determined by laboratory tests and should repre- sent the conditions to be expected during various seasons of the year; is determined by judgment. It may be 30 per cent or 50 per cent or more as previously explained; t is determined by float tests or other measurements of the stream flow; k is determined by laboratory tests in which mix- tures of various strengths are incubated for vari- ous periods of time. Different values of k will be obtained for different characteristics of the sewage; but for the same sewage the value of k should be unchanged for different periods of incubation. Rideal devised the formula: l XO=C(M-N)S in which -X" = flow of the stream expressed in second feet; = grams of free oxygen in one cubic foot of water; S =rate of sewage discharge in second feet; M= grams of oxygen required to consume the organic matter in one cubic foot of diluted sewage as determined by the permanganate test with 4 hours boiling; N = grams of oxygen available in the nitrites and nitrates in one cubic foot of diluted sewage; C= ratio between the amount of oxygen in the stream and that required to prevent putrefaction. Where C is equal to or greater than one, satisfactory conditions have been attained. 1 From " Sewage," by Samuel Rideal, 1900, p. 16. 380 DISPOSAL BY DILUTION In using this formula it is necessary to make analyses of trial mixtures of sewage and water until the correct mixture has been found. Hazen's formula is: 1 __ ~S" 0' in which D = dilution ratio; x = volume of water; S = volume of sewage; m= result of the oxygen consumed test expressed in p. p.m. after 5 minutes, boiling with potassium permanganate ; = amount of dissolved oxygen in the diluting water expressed in p. p.m. For comparison with Rideal's formula the factor of 7 should be used instead of 4 to allow for the increased time of boiling. Since the amount of oxygen needed is dependent on the amount of organic matter in the sewage rather than the total volume of the sewage, and since the amount of organic matter is closely proportional to the population, the amount of diluting water has sometimes been expressed in terms of the population. Bering's recommendation for the quantity of diluting water necessary for Chicago sewage was 3.3 cubic feet of water per second per thousand population. Experience has proven this to be too small. Between a minimum limit of 2 second-feet and a maximum of 8 second-feet of diluting water per thousand population the success of dilution is uncertain. Above this limit success is practically assured and below this limit failure can be expected. Even with these carefully devised formulas and empirical guides, the factors of reaeration, dilution, sedimentation, tem- perature, etc., may have so great an effect as to vitiate the con- clusions. As shown in Table 75 dilution in winter is far more successful than in summer. The lower temperatures so reduce the activity of the putrefying organisms that consumption of oxygen is greatly retarded. 225. Governmental Control. A comprehensive discussion of the legal principles governing the pollution of inland waters 1 See Am. Civil Engineers' Pocket Book, Second Edition, p. 982. PRELIMINARY TREATMENT 381 is contained in "'A Review of the Laws Forbidding the Pollution of Inland Waters," by E. B. Goodell, published by the United States Geological Survey in 1905, as Water Supply Paper No. 152. The disposal of sewage by dilution is subject to statutory limitations in many states. The enforcement of these laws is usually in the hands of the state board of health, which is fre- quently given discretionary powers to recommend and some- times to enforce measures for the abatement of an actual or potential nuisance. Such recommendations usually take the form of a specification of certain forms of treatment preliminary to disposal by dilution. No project for the disposal of sewage by dilution should be consummated until the local, state, national, and in the case of boundary waters, international laws have been complied with. The attitude of the courts in dif- ferent states has not been uniform. Little guidance can be taken from the personal feeling of the persons immediately interested. The opinion of the riparian owner 5 miles down stream may differ materially from the popular will of the voters of a city, and it is likely to receive a more favorable hearing from the court. Statutes and legal precedents are the safest guides. 226. Preliminary Treatment. If the sewage to be disposed of by dilution contains unsightly floating matter, oil, or grease, no amount of oxygen in the diluting water will prevent a nuisance to sight, or the formation of putrefying sludge banks. Under such conditions it will be necessary to introduce screens or sedi- mentation basins, or both, in order to remove the floating and the settling solids. Biologic tanks, filtration, or other methods of treatment may be necessary for the removal of other undesirable constituents. 227. Preliminary Investigations. Before adopting disposal of sewage by dilution without preliminary treatment, or before considering the proper form of treatment necessary to render disposal by dilution successful, a study should be made of the character of the body of water into which the sewage or effluent is to be discharged. This study should include: measurements of th? quantity of water available at all seasons of the year; analyses of the diluting water to determine particularly the available dissolved oxygen: observations of the velocity and direction of currents, and the effect of winds thereon: a study of the effect on public water supplies, bathing beaches, fish life, 382 DISPOSAL BY DILUTION etc. Good judgment, aided by the proper interpretation of such information should lead to the most desirable location for the sewer outlet. If preliminary treatment is found to be neces- sary tests should be made to determine the necessary extent and thoroughness of the treatment. CHAPTER XV SCREENING AND SEDIMENTATION 228. Purpose. The first step in the treatment of sewage is usually that of coarse screening in order to remove the larger particles of floating or suspended matter. Screens and sedi- mentation basins are used to prevent the clogging of sewers, channels, and treatment plants; to avoid clogging of and injuries to machinery; to overcome the accumulation of putrefying sludge banks; to minimize the absorption of oxygen in diluting water; and to intercept unsightly floating matter. By the plain sedimentation of sewage is meant the removal of suspended matter by quiescent subsidence unaffected by septic action or the addition of chemicals or other precipitants. In order to prevent septic action plain sedimentation tanks must be cleaned as frequently as once or twice a week in warm weather but not quite so often in cold weather. Fine screening may take the place of sedimentation where insufficient space is available for sedimentation tanks, and it is desired to remove only a small portion of the suspended matter. Recent American practice has tended to restrict the field of fine screening to treatment requiring less than 10 per cent removal of suspended matter, thus eliminating screens from the field covered by plain sedimentation tanks. The practice is well expressed by Potter, who states: 1 Where a high degree of purification is sought, the use of fine screens is of doubtful value. A modern settling tank will give better results and at a less cost for a given degree of purification. A settled liquid is also superior to a screened liquid for subsequent biological treatment in filters. . . . Again the storing of large quantities of screenings must necessarily be more objectionable than the storing of the digested sludge of a modern settling tank. 1 Trans. Am. Society Civil Engineers, Vol. 58, 1907, p. 988. 383 384 SCREENING AND SEDIMENTATION 229. Types of Screens. The definitions of some types of screens as proposed by the American Public Health Association follow: A bar screen is composed of parallel bars or rods. A mesh screen is composed of a fabric, usually wire. A grating consists of 2 sets of parallel bars in the same plane in sets inter- secting at right angles. A band screen consists of an endless perforated band or belt which passes over upper and lower rollers. A perforated plate screen is made of an endless band of perforated plates similar to a band screen. A wing screen has radial vanes uniformly spaced which rotate on a horizontal axis. A disc screen consists of a circular perforated disc with or without a central truncated cone of similar material mounted f.-Band Screen. 2.- Wing Screen. 3.- Shove! -Vane Screen. 4.- Drum Screen. 5-Riensch-Wurl Screen. FIG. 150. Types of Moving Screens. Trans. Am. Society Civil Engineers, Vol. 78, 1915, p. 893. in the center. The Reinsch Wurl screen is the best known type of disc screen. A cage screen 1 consists of a rectangular box made up of parallel bars with the upstream side of the box or cage omitted. Allen 2 gives the following definitions: A drum screen is a cylinder or cone of perforated plates or wire mesh which rotates on a horizontal axis. A shovel vane screen is similar to a wing screen with semicircular wings and a different method of removing the screenings. Examples of a band screen, a wing screen, a shovel vane screen, a drum screen and a disc 1 Not defined by the American Public Health Association. 2 Trans. Am. Society Civil Engineers, Vol. 78, 1915, p. 892. TYPES OF SCREENS 385 screen are shown in Fig. 150. A bar screen is shown in Fig. 151 and a cage screen is shown in Fig. 152. Direction of Flow 1 I 1--- -.:.:.:.. 1 1 \ Side View. Front View Looking down Stream. FIG. 151. Sketch of a Bar Screen. Screens can be classed as fixed, movable, or moving. Fixed screens are permanently set in position and must be cleaned by rakes or teeth that are pulled between the bars. Movable screens are stationary when in operation, but are lifted from the sewage for the purpose of cleaning. Moving screens are in continuous motion when in operation and are cleaned while in motion. Fixed bar screens may be set either vertical, in- clined, or horizontal. Movable screens with a cage or box at the bottom are sometimes used. Ihe box should be of solid material to prevent the forcing of FIG. 152. Sketch of a Cage Screen. screenings through it when the screen is being raised for cleaning. A mesh screen should be used only under special circumstances because of the difficulty in cleaning. Screens which must be raised from the sewage for cleaning should be 386 SCREENING AND SEDIMENTATION arranged in pairs in order that one may be working when the other is being cleaned. Movable screens are undesirable for small plants because the labor involved in raising and lowering is greater than in cleaning with a rake and the screens are more likely to be neglected. In a large plant rakes operated by hand are too small for cleaning the screens. A fixed screen is sometimes used with moving teeth fastened to endless chains. The teeth pass between the parallel bars and comb out the screenings. If the screen chamber in a small plant is too deep for accessibility a movable cage or box screen may be desirable. Moving screens are generally of fine mesh or perforated plates. They are kept moving in order to allow continuous cleaning. They are cleaned by brushes or by jets of air, water, or steam. 230. Sizes of Openings. The area or size of the opening of a screen is dependent upon the character of the sewage to be treated and upon the object to be attained. Large screens, with openings between 1^ inches and 6 inches are used to protect centrifugal pumps, tanks, automatic dosing devices, conduits, and gate valves from large objects such as pieces of timber, dead animals, etc., which are found in sewage. The quantity of material removed is variable, and is usually small. Medium-size screens with openings from J inch to 1J inches are used to prepare sewage for passage through reciprocating pumps, complex dosing apparatus, contact beds, and sand filters. The amount of material removed varies from 0.5 to 10 cubic feet per million gallons of sewage treated, dependent on the character of the sewage and the size of the screen. Screenings before drying contain 75 to 90 per cent moisture and weigh 40 to 50 pounds per cubic foot. At times the amount removed may vary widely from the limits stated. Schaetzle and Davis 1 state: Screenings differ greatly both in amount and character. . . . The amount varies with the days of the week as well as during the course of the day. It reaches its maximum about noon or shortly before and commences to disappear about midnight, reaching a mimimum about 4 or 5 A.M. The material is almost wholly organic and 1 Removal of Suspended Matter by Sewage Screens, Cornell Civil En- gineer, 1914. Abstracted in Engineering and Contracting, Vol. 41, 1914, p. 451. SIZES OF OPENINGS 387 consists of scraps of vegetables or fruit, cloth, hair, wood, paper and lumps of fecal matter. The amount varies so widely that it is impossible to state just what to expect any definite size screen to remove. The amount of water contained is small compared with that in the sludge in sedimentation basins and amounts to from 70 per cent to 80 per cent. On account of its organic origin it is highly putrescible. Medium-size screens are sometimes placed close together with the bars of the. one opposite the openings in the other, thus approaching a fine screen. Fine screens vary in size of opening from J inch to 50 open- ings per linear inch or 2,500 per square inch. They are used for removing solids preparatory to disposal by dilution, to protect sprinkling filters, complex dosing apparatus, sand filters, sewage farms, and to prevent the formation of scum in subsequent tank treatment. In general, fine screens will remove from 0.1 to 1 cubic yard of wet material per million gallons of sewage treated. The wet screenings will contain about 75 per cent moisture and will weigh about 60 pounds per cubic foot. The dry weight of the screenings will therefore be about 10 to 400 pounds per million gallons of sewage treated. The effect of the removal of this amount of material is usually not detectable by methods of chemical analysis, the amount of suspended matter before and after screening being found unchanged. In his conclusions on the discussion of the results to be expected from fine screens, Allen states: 1 With openings not more than 0.1 inch in size, fine screening should remove at least 30 per cent of the sus- pended solids and 20 per cent of the suspended organic solids from ordinary domestic sewage, or 0.1 cubic yard of screenings, containing 75 per cent water per thousand population daily, The effect of the use of different size openings under the same conditions is shown in Fig. 153. 2 Some data covering the amount of material removed by screening are given in Table 76. More 1 " The Clarification of Sewage by Fine Screens," Trans. Am. Society Civil Engineers, Vol. 78, 1915, p. 1000. 2 Langdon Pearse, Trans. Am. Society Civil Engineers, Vol. 78, 1915, p. 1000. 388 SCREENING AND SEDIMENTATION . 13 -s 8 13 O J (S 1 1 II II > o ^> +i oo :-H .^ :S 7 C Oi _, O O CO rji OS OO ,OOOOOi-H| oo ;o'ooooo'co > ^ T}< 1C co co ooo^o s I-H co (N ^ -*o ?Ci ^_ | 1C c O CO o l> 'OOOOO econ- FIG. 155. Grit Chamber at Cleveland, Ohio. Eng. Record, Vol. 73, 1916, p. 409. n * ,-Welr .tflt'Steel CiSOIbs. ~~ """^^' P*" S l6cks r ,Screen ' 2 l 6 ',. ncf *K&~Ls.H l fluan VJl II f&g ., r4'^7/ /tf L I -?WS*- J _ I Chamber" ,6-MKp. -|r / Open Join fs :;;[[ Screen Se/ectrt DryFi'lling in Layers^ Plan. Wj/'r Penstocks By-pan . . Valve ^ft tl rT r* n jj j To Effluent Pipe from Sludge Beds i-'l"J Cross Section.'' FIG. 156. Grit Chamber at Hamilton, Ontario. Eng. News, Vol. 73, 1915, p. 425. 400 SCREENING AND SEDIMENTATION without stopping the sewage flow. The details of the chamber at Hamilton, Ontario, are shown in Fig. 156. In studying these drawings the following features should be noted: 1st, the smooth curves in the channel to prevent eddies, undue deposition of organic matter, and difficulties in cleaning; 2nd, the hopper in the upper end of the grit storage chamber and the slope of the bot- tom of at least 1 : 20 ; and 3rd, the simplicity of the inlet and out- let devices which may be either stop planks or cast iron sluice gates. The drawings shown are merely representative of some sat- isfactory 7 types. The number and variety of grit chambers in existence is great. In designing grit chambers consideration must be given to the method of cleaning. They are ordinarily cleaned by such methods as have been described for the cleaning of catch-basins in Chapter XII. Continuous bucket scrapers similar to excavating machines are sometimes used for the clean- ing of large grit chambers. The period between cleanings is variable. The design should be such as not to require more frequent cleanings than twice a month under the worst conditions. The fluctuations in quality and quantity of grit will vary the period between cleanings. 238. Number of Grit Chambers. The period of retention in grit chambers is so short and the velocity of flow so near the maximum and minimum limitations that the wide fluctuations in the rate of discharge in storm and combined sewers necessi- tates the construction of a number of chambers which should be operated in parallel in order to maintain the velocity between th^ proper limits. Unless arrangements are made permitting the cleaning of grit chambers during operation, more than one grit chamber should be installed in order that when one is being cleaned the others may be in operation. The number of grit chambers must be determined by the desired conditions of operation and the cost of construction. The larger the number of basins the more nearly the flow in any one basin can be maintained constant, but the more expensive the construction. The increase in velocity of flow with increasing quantity is dependent on the outlet arrangements. In a shallow chamber with vertical sides and a standard sharp-crested rectangular weir at the outlet the velocity will vary approximately as the cube root of the rate of flow. Similarly if the outlet is a V notch the QUANTITY AND CHARACTERISTICS OF SLUDGE 401 velocity will vary as the fifth root of the rate of flow. In all cases the deeper the basin the more nearly the velocity varies directly as the rate of flow. The outlet weir can be arranged as at Cleveland, so that the velocity remains constant for all rates of flow within certain limits. It is seldom that more than three grit chambers are necessary to care for the fluctuations in flow. 239. Quantity and Characteristics of Sludge from Plain Sedimentation. The sludge removed from plain sedimentation basins is slimy, offensive, not easily dried, and is highly putres- cible and odoriferous. It contains about 90 per cent moisture and has a specific gravity from 1.01 to 1.05. The amount removed varies between 2 and 5 cubic yards per million gallons of sewage. The percentage of suspended matter removed varies between 20 and 60. The total amount removed and the percentage removal depend on the character of the sewage, the type of basin, and the period of detention. 240. Dimensions of Sedimentation Basins. The dimensions of a sedimentation basin are determined by a method similar to the one given for the determination of the dimensions of a grit chamber in Art. 236. . The capacity of the basin is first fixed upon to give the required period of sedimentation and sludge storage capacity. The length of the basin is the product of the velocity and the period of retention. The length, width, and depth of the basin are normally fixed by considerations of economy and the limitations of the local conditions, such as available area, topography, foundations, etc., and examples of good practice. A study of basins in use shows the relation between length and width to vary normally between 2:1 and 4:1. Widths greater than 30 to 50 feet are undesirable because of the danger of cross currents and back eddies which will reduce the efficiency of the sedimentation. Depths used in practice vary too widely to act as guides for any particular design. Theo- retically the shallower the basin the better the result. Tanks abroad have been built as shallow as 3 feet and some in this country as deep as 16 feet. The economical dimensions can be determined by trial or by calculus. They will serve as a guide in the adoption of the final dimensions. The method to be pursued in determining the economical dimensions of any engineering structure are : 402 SCREENING AND SEDIMENTATION b- I. Express the total cost of the structure in terms of as few variables as possible. II. Express all of the variables in terms of any one and rewrite the expression for the total cost in terms of this one variable. III. Equate the first derivative of the expression with regard to this variable to zero and solve for the variable. The result will be the economical value of the variable. The values of the other variables can be computed from the relations already expressed. For example, let it be desired to determine the dimen- sions of two continuous-flow sedimentation basins as shown in Fig. 157, in which the period of retention in each is to be 2 hours, the veloc- ~* ity of flow is not to ex- ceed one foot per second, i and the sludge accumula- 1 ted will be 3 cubic yards per million gallons of sew- i age treated. The quantity of sewage to be treated "* is 18,000,000 gallons per FlG - 157. Diagram for the Compu- day. The shortest time tation of Economical Basin Di- between cleanings will be mensions. 2 weeks. The capacity of each basin must be 2/24 of 18,000,000 gallons, or 200,000 cubic feet in order to allow a period of retention of 2 hours. To this volume should be added sufficient capacity to allow for the 2 weeks of sludge stor- age between cleanings. When a basin is being cleaned the load must be put on the remaining basins. Then if Q represents the rate of accumulation of sludge per day, n represents the number of days between cleanings, m represents the number of basins, and s the sludge capacity of one basin, then s= Q(n-l) , Q m ml' The sludge storage capacity for the example given will be approximately 11,000 cubic feet. In expressing the total cost of the basins let h = the depth in feet. I =the length in feet. b =the width in feet. DIMENSIONS OF SEDIMENTATION BASINS 403 The cost of land, floor, etc., per square foot =p dollars. The cost of wall per foot length =qh 2 dollars. The cost of pipes, valves and appurtenances = P dollars. Then the total cost C = (3l+4b)qh 2 +2plb+P. It is now necessary to express the three variables 6, Z, and h, in terms of one of them. From the relation Q = 2blh it is possible to rewrite the expression for the total cost as: Holding h constant and differentiating with regard to 6 in the first expression and with regard to I in the second expression, equating to zero and solving we get: -V3 an -VI- The economical relation between 6 and I is therefore 6=0.75? regardless of the value of h. Substituting these values of I and b in the original expression for the total cost, it becomes Differentiating with regard to h, equating to zero, and solving g / In the example given if q =0 . 2 and p = 1 . then h = 11 . 6 feet, 6 = 120 feet and I = 160 feet. Since these are reasonable dimensions and in accord with good practice they should be used, unless other conditions are unsuit- able or the velocity of flow is too great. A width of channel of 120 feet as compared to a length of 160 feet is conducive to a poor distribution of velocity across the basin. A ratio of width to length of about 1:4 is desirable. In this case, by the use of three baffles parallel to the length of the basin, thus dividing it into channels 40 feet wide and 11.6 feet deep, the ratio of width to length is changed to 1 : 4 and the velocity will be 404 SCREENING AND SEDIMENTATION increased only to 0.06 foot per second or 3.6 feet per minute, which is a reasonable velocity. It could be reduced by increasing the spacing of the baffles or the depth of the chamber. Complicated baffling is undesirable. Two or three overflow baffles may be used to permit quiescent sedimentation in the space thus formed, and hanging baffles may be placed before the inlet and outlet to break up surface currents, or to prevent the movement of scum. The hanging baffles should not extend more than 12 to 18 inches below the water surface. The inlet and outlet are sometimes arranged to permit the reversal of flow, and the connecting channels between basins to allow the opera- tion of any number of basins in series or in parallel, although such arrangements are more important in water purification. Sewage should enter and leave at the top of the basin. Cleaning is facilitated by the location of a central gutter in the bottom of the basin with the slope of the bottom of the basin towards the gutter from 1 : 25 to 1 : 80 or steeper. A pipe, 2 inches or larger in diameter, containing water under pres- sure with connections for hose placed at frequent intervals is a useful adjunct in flushing the sludge from the sedimentation basins. For equal capacity, deer vertical flow tanks are more expensive and difficult to con- struct than the shallower rect- angular type. Deep tanks are advantageous, however, in that sludge can sometimes be re- moved by gravity or by pump- ing without stopping the opera- tion of the tank. They will also operate successfully with shorter periods of detention and higher velocities. The up- ward velocity should not be greater than the velocity of sedimentation of the smallest particle to be removed. The them will be increased by the FIG. 158. Section through a Dort- mund Tank. Depth 20 to 30 feet. efficiency of sedimentation in sedimentation of the larger particles which drag some of the smaller particles down with them. The Dortmund tank shown in Fig. 158 is an example of this type. CHEMICALS 405 Ordinarily it is not necessary to roof sedimentation basins as the odors created are not strong, and difficulties with ice are seldom serious. CHEMICAL PRECIPITATION 241. The Process. Chemical precipitation consists in adding to the sewage such chemicals as will, by reaction with each other and the constituents of the sewage, produce a flocculent precipi- tate and thus hasten sedimentation. The advantages of this process over plain sedimentation are a more rapid and thorough removal of suspended matter. Its disadvantages include the accumulation of a large amount of sludge, the necessity for skilled attendance, and the expense of chemicals. The process is not in extensive use as the conditions under which the advantages outweigh the disadvantages are unusual. Sewage containing large quantities of substances which will react with a small amount of an added chemical to produce the required precipitate are the most favorable for this method of treatment. Chemical precipitation accomplishes the same result as plain sedimentation, although the effluent from the chemically pre- cipitated sewage may be of better quality than that from a plain sedimentation basin. 242. Chemicals. Lime is practically the only chemical used for the precipitation of the solid matter in sewage. Commercial lime used for precipitation consists of calcium oxide (CaO), with large quantities of impurities. It should be stored in a dry place and protected from undue exposure to the air to prevent the formation of calcium carbonate (CaCOs), the formation of which is commonly known as air slacking. The active work in the formation of the precipitate is performed by the lime (CaO) or calcium hydroxide (Ca(OH)2). The lime should therefore be purchased on the basis of available CaO, which may be as low as 10 to 15 per cent in some commercial products. The amount of lime necessary depends on the quality of the sewage, the period of retention in the sedimentation basin, the method of application, the required results, and other less easily measured factors. Full scale tests for the amount of lime needed to produce certain results are the most satisfactory. In practice the amount of lime necessary when lime alone is used as a pre- 406 SCREENING AND SEDIMENTATION cipitant has been found to be about 15 grains per gallon. This may be markedly different, dependent on the quality of the sewage. For acid sewages, lime alone is not suitable as a pre- cipitant since it is necessary to add sufficient lime to neutralize the sewage before the calcium carbonate will be precipitated. The use of copperas (FeSCU) together with lime, leads to economy in the use of chemicals as the flocculent precipitate of ferrous hydroxide (Fe(OH)2) is more voluminous than the precipitate of calcium carbonate. This is commonly known as the lime and iron process. The presence of iron in certain trade wastes may reduce the cost of chemical precipitation, as the necessary amount of copperas is reduced. Where 15 grains of lime alone will be needed per gallon of sewage, the total amount of chemicals used will be reduced to 8 to 10 grains per gallon with the use of lime and iron. This combination is less expensive than the use of lime alone, and is even cheaper where the iron is already present in the sewage. Such a condition is well illus- trated by the sewage at Worcester, Mass., -where the oldest and best known chemical precipitation plant in the United States is located. The amount of lime used at this plant has varied between 6 and 10 grains per gallon of sewage, the normal amount being about 7 grains. No iron is added because of the amount already in solution. The results of a series of experiments on the chemical precipi- tation of sewage by Allen Hazen, are given in the 1890 Report of the Massachusetts State Board of Health, on p. 737 of the volume on the Purification of Water and Sewage. Hazen con- cludes as the result of his experiments: concerning lime, There is a certain definite amount of lime . . . which gives as good or better results than either more or less. This amount is that which exactly suffices to form normal carbonates with all the carbonic acid of the sewage. This amount can be determined in a few minutes by simple titration. Concerning lime and iron (copperas) he states: Ordinary house sewage is not sufficiently alkaline to precipitate copperas, and a small amount of lime must be added to obtain good results. The quantity of lime required depends both upon the composition of the sewage and the amount of copperas used, and can be calculated PREPARATION AND ADDITION OF CHEMICALS 407 from titration of the sewage. Very imperfect results are obtained from too little lime, and, when too much is used, the excess is wasted, the result being the same as with a smaller quantity. In precipitation by ferric sulphate and crude alum, the addition of lime was found unnecessary, as ordinary sewage contains enough alkali to decompose these salts. Within reasonable limits the more of these precipitants used the better is the result, but with very large quanti- ties the improvement does not compare with the increased cost. Using equal values of different precipitants, applied under the most favorable conditions for each, upon the same sewage, the best results were obtained from ferric sulphate. Nearly as good results were obtained from copperas and lime used together, while lime and alum each gave somewhat inferior effluents. . . . When lime is used there is always so much lime left in solution that it is doubtful if its use would ever be found satisfactory except in case of an acid sewage. It is quite impossible to obtain effluents by chemical precipitation which will compare in organic purity with those obtained by intermittent nitration through sand. It is possible to remove from one-half to two-thirds of the organic matter by precipitation . . . and it seems probable that ... a result may be obtained which will effectually prevent a public nuisance. 243. Preparation and Addition of Chemicals. Lime is not readily soluble in water. Therefore, it is not best to add the lime as a powder to the sewage, but to form a milk of lime, that is, a supersaturated solution containing from 2,000 to ; 4,000 grains per gallon, although dry slaked lime has sometimes been applied directly. The solution is prepared in tanks in a quantity sufficient for some part of the day's run, commonly sufficient to last through one shift of 8 or 10 hours. The lime is prepared by placing the amount necessary to fill one storage tank into a slaking tank containing some cold water. Sufficient water is added to keep the solution just at the boiling point, or steam may be added to make it boil. After slaking, it is run into the milk-of-Ume solu- tion tank and sufficient water added to bring to the proper strength. The milk of lime is added in measured quantities, being controlled by a variable head on a fixed orifice or weir, so that it may be varied with the amount of sewage flowing through the plant. The amount of lime to be added is determined by 408 SCREENING AND SEDIMENTATION titration with phenolphthalein, experience indicating the color to be obtained when the proper amount of lime has been added. The use of either copperas or alum has been so rare, for the precipitation of sewage, that a description of the methods of handling these chemicals as a sewage precipitant is not war- ranted. An excellent description of the methods of handling these chemicals in water purification will be found in " Water Purification " by Ellms. TABLE 81 RESULTS OP CHEMICAL PRECIPITATION AT WORCESTER, MASSACHUSETTS* 1900 1910 1920 Amount of sewage treated, million gallons 4,781 5,317 8,893 Amount of sewage chemically treated, million gallons Gallons of wet sludge per million gallons of sewage treated 3,650 3,574 4,450 7,300 4 185 Per cent of solids in sludge 4.42 8 20 4 64t Tons of solids 7,294 4,182 6431f Pounds of lime added per million gallons of sewage pumped Per cent of organic matter removed : By albuminoid ammonia: Total 999 52 7t 762f 58 4 534 51 9 Suspended 90.0J 88.7 83 6 By oxygen consumed : Total 62 8t 61 1 62 5 Suspended 86. 6{ 89.7 86 2 * Computed from Annual Report ot the Superintendent of Sewers, Nov. 30, 1919, and 1920. t These figures are for 1919. J These figures are for 1902. These figures are for 1905. 244. Results. The results of Hazen's experiments indicate that a greater amount of suspended matter can be removed in the same time by chemical precipitation than by plain sedimen- tation. The percentage of removal of suspended matter may be as high as 80 to 90 per cent with a period of retention of 6 to 8 hours and the addition of a proper amount of chemical. That RESULTS 409 the method is not always a success is shown by the results of some tests at Canton, Ohio. 1 The report states: .... lime treatment removes about 50 per cent of the suspended matter, and in the main about 50 per cent of the organic matter. . . . These data are instructive as indicating that the addition of lime to the Canton sewage in quantities as previously stated does not materi- ally improve the character of the resulting effluent over and above that which could be produced by plain sedi- mentation alone. The plant at Worcester, Mass., is the largest in the United States and information from it is of value. A summary of the results at Worcester for 1900, 1910, and 1920 are shown in Table 81. 1 Report of the Ohio State Board of Health, 1908, page 425. CHAPTER XVI SEPTICIZATION 245. The Process. Septic action is a biological process caused by the activity of obligatory or facultative anaerobes as the result of which certain organic compounds are reduced from higher to lower conditions of oxidation, some of the solid organic substances are rendered soluble, and a quantity of gas is given off. Among these gases are: methane, hydrogen sulphide, and ammonia. The biologic process in the septic tank represents the downward portion of the cycle of life and death, in which complex organic compounds are reduced to a more simple condition available as food for low forms of plant life. The disposal of sewage by septic action, when introduced, promised the solution of all problems in sewage treatment. Septic action is now better understood, and it is known that some of the early claims were unfounded. The principal advantage of septic action in sewage treatment is the relatively small amount of sludge which must be cared for compared to that produced by a plain sedimentation tank. The sludge from a septic tank may be 25 to 30 per cent and in some cases 40 per cent less in weight, and 75 to 80 per cent less in volume than the sludge from a plain sedimentation tank. The most important results of septic action and the greatest septic activity occur in the deposited organic matter or sludge. The biologic changes due to septic action which occur in the liquid portion of the tank contents are of little or no importance. The installation of a septic tank, although it may fail to prevent the nuisance calling for abatement, has a remarkable psycho- logical effect in stilling complaints. Among other advantages are the comparative inexpensiveness of the tanks and the small amount of attention and skilled attendance required. The tanks need cleaning once in 6 months to a year. If properly designed no other attention is necessary. 410 THE SEPTIC TANK 411 The septic tank has fallen into some disrepute because of the better results obtainable by other methods, the occasional dis- charge of effluents worse than the influent, the occasional dis- charge of sludge in the effluent caused by too violent septic boiling, and on account of patent litigation. This last difficulty has been overcome as the Cameron patents expired in 1916. Occasionally the odors given off by the septic process are highly objectionable and are carried for a long distance. These odors can be controlled to a large extent by housing the tanks. Over-septicization must be guarded against as an over-septicized effluent is more difficult of further treatment or of disposal than a comparatively fresh, untreated sewage. An over-septicized or stale sewage is indi- cated by the presence of large quantities of ammonias, either free or albuminoid, frequently accompanied by hydrogen sul- phide and other foul-smelling gases. The oxygen demand in an over-septicized sewage is greater than that in a fresh or more carefully treated sewage. 246. The Septic Tank. A septic tank is a horizontal, continu- ous-flow, one-story sedimentation tank through which sewage is allowed to flow slowly to permit suspended matter to settle to the bottom where it is retained until anaerobic decomposition is established, resulting in the changing of some of the suspended organic matter into liquid and gaseous substances, and a conse- quent reduction in the quantity of sludge to be disposed of. 1 It is to be noted that a continuous flow is essential to a septic tank. Small tanks containing stagnant household sewage are called cess- pools, although sometimes erroneously spoken of as septic tanks. Septic and sedimentation tanks differ in their method of opera- tion only in the period of storage and the frequency of cleaning. The period of flow in a septic tank is longer and it is cleaned less frequently. The results obtained by the two processes differ widely. A septic tank can be converted into a sedimentation tank, or vice versa, by changing the method of operation, no constructional features requiring alteration. The purpose of the tank is to store the sludge for such a period of time that partial liquefaction of the sludge may take place, and thus minimize the difficulty of sludge disposal. For this reason the sludge storage capacity of a septic tank is sometimes greater than would be necessary for a plain sedimentation tank. 1 Definition proposed by the Am. Public Health Assn. 412 SEPTICIZATION al B "^ 8 So fo r O ^ 11 I? 1 -HtNCO COCOOO COO5CO I 0500 I-H.-H Oi OO 00 1C I rH t- CO 1-1 N ec^cc <>CD COCO i 1 St>.i-H OS It-^-l 1C 00 i-H O COCOiO O >COiO CO ^ ^ ^O5CO O a 38' lOO OOi-l OO ^HIO--H odi>oo di-i rH O C3 CO i-l i-l i-l OOCO (M >O ooo oooo odio'iN IM'^ |>O OCO(N CO i-HfH O500 rt^H O5O> O5OOO t>-i-H O5OOO tO( Section. FIG. 160. Design for a Residential Septic Tank for a Family of Ten. Illinois State Board of Health. IMHOFF TANKS 417 Small septic tanks for rural homes of 5 to 15 persons, Or on a slightly larger scale for country schools and small institutions, are little more than glorified cesspools. Nevertheless much attention has been given to the construction of such tanks by the National Government and by state boards of health. 1 The recommendations of some of these boards have been compiled in Table 84. A typical method for the construction of such tanks, as recommended by the Illinois State Board of Health, is shown in Fig. 160. A subsurface filter, into which the effluent is dis- charged, is an important adjunct where no adequate stream is available to receive the discharge from the tank. TABLE 84 CAPACITIES OF SEPTIC TANKS FOE SMALL INSTALLATIONS Rule Recommended by State Board of Health Number, Persons Capacity, Gallons per Person Period of Retention Remarks Wisconsin Ohio . . . 4 to 10 30 50 24 hours Not less than 560 gallons 24 to 48 hours Texas 24 hours Illinois U. S. Dept. Agriculture. North Carolina Large 45 40 1 15 24 hours 24 hours 25 per cent additional capacity for sludge Not less than 500 gallons North Carolina North Carolina North Carolina Schools 20 pupils Medium School Homes / 25 } 20 25 to 30 249. Imhoff Tanks. In the discussion of septic tanks it has been brought out that one of the objections to their use is the unloading of sludge into the effluent which occasionally causes a greater amount of suspended matter iri the effluent than in the influent. The Imhoff tank is a form of septic tank so arranged that this difficulty is overcome. It combines the advantages of the septic and sedimentation tanks and overcomes some of their disadvantages. An Imhoff tank is a device for the treatment of sewage, consisting of a tank divided into 3 compartments. The upper compartment is called the sedimentation chamber. In 1 Sewage Treatment from Single Houses and Small Communities, by L. C. Frank. U. S. Public Health Service, Bulletin 101, 1920. 418 SEPTICIZATION it the sedimentation of suspended solids causes them to drop through a slot in the bottom of the chamber to the lower com- partment called the digestion chamber. In this chamber the solid matter is humified by an action similar to that in a plain septic tank. The generated gases escape from the digestion chamber to the surface through the third compartment called the transition or scum chamber. Sections of Imhoff tanks are shown in Fig. 161. It is essential to the construction of an Imhoff tank that the slot in the bottom of the sedimentation chamber does not permit Effect of Design on Sludge-Storage Capacity. (AandB) Original Design of Imhoff lank Downward and Upward FlowTank FIG. 161. Typical Sections through Imhoff Tanks. Eng. News, Vol. 75, p. 15. the return of gases through the sedimentation chamber, and that there be no flow in the digestion chamber. The Imhoff tank was invented by Dr. Karl Imhoff, director of the Emscher Sewerage District in Germany. Its design is patented in the United States, the control of the patent being in the hands of the Pacific Flush Tank Co. of Chicago, which collects the royalties which are payable when construction work begins. The fee for a tank serving 100 persons is $10, for 1,000 persons is $80 and for 100,000 persons is $2550. The rate of the royalty reduces in proportion as the number of persons served increases. 1 As designed by Imhoff and used in Germany the tanks were of the radial flow type and quite deep. The depth, as 1 Eng. News Record, Vol. 78, 1917, p. 566. DESIGN OF IMHOFF TANKS 419 explained by Imhoff, is one of the chief requirements for the successful operation of the tank. As adapted to American practice the tanks are generally of the longitudinal flow type and are not made so deep. An isometric view of a radial flow Imhoff tank is shown in Fig. 162. The sewage enters at the center of the tank near the surface and flows radially outward under the scum ring and over a weir placed near the circum- ference of the tank. One type of longitudinal flow tank is shown in isometric view in Fig. 163. -. r r~Sludqe Outlet Pipe Channelto Sludge Bed \Sedimenfation Comp'f. \&m 5 . m - 40- Weirs^ Gas Stack Distribut ' Cha' - Sludge Corfip't ff* ''Gravel FIG. 162. Sketch of Radial Flow Imhoff Tank at Baltimore, Maryland. Eng. Record, Vol. 70, p. 5. 250. Design of Imhoff Tanks. The velocity of flow, period of retention, and the quantity of sewage to be treated determine the dimensions of the sedimentation chamber as in other forms of tanks. The velocity of flow should not exceed one foot per minute, with a period of retention of 2 to 3 hours. A greater velocity than one foot per minute results in less efficient sedi- mentation. A longer period of retention than the approximate limit set may result in a septic or stale effluent, and a shorter period may result in loss of efficiency of sedimentation. The bottom of the sedimentation chamber should slope not less than 1 J vertical to 1 horizontal, in order that deposited material will descend into the sludge digestion chamber. Provision should be made for cleaning these sloping surfaces by placing a walk on the top of the tank from which a squeegee can be handled to push down accumulated deposits. It is desirable to make the material of the sides and bottom of the sedimenta- 420 SEPTICIZATION tion chamber as smooth as possible to assist in preventing the retention of sludge in the sedimentation chamber. Wood, glass, and concrete have been used. The latter is the more common and has been found to be satisfactory. The length of the sedi- mentation chamber is fixed by the velocity of flow and the period of retention. Tanks are seldom built over 100 feet in 'Stop Plank ^ Outlet Channel for Reverse Flow f-'-Sfop Plank Outlet .--Tie Beams -- Baffle Wall *'" .'-Equalizing - Port InletChannel, Direct Flow or Outlet Channel, Reverse Flow Brace, 10-0" C.toC. Reinforced Concrete Walls and Partitions. Reducer Iron Supports - FIG. 163. Isometric View of Longitudinal Flow Imhoff Tank at Cleburne, Texas. Eng. News, Vol. 76, p. 1029. length, however, because of the resulting unevenness in the accu- mulation of sludge. Where longer flows are desired two or more tanks may be operated in series. The width of the chamber is fixed by considerations of economy and convenience. It should not be made so great as to permit cross currents. In general a narrow chamber is desirable. Satisfactory chambers have been constructed at depths between 5 and 15 feet. The DESIGN OF IMHOFF TANKS 421 depth of the sedimentation chamber and the depth of the diges- tion chamber each equal about one-half of the total depth of the tank. This should be made as deep as possible up to a limit of 30 to 35 feet, with due consideration of the difficulties of excavation. C. F. Mebus states: 1 In 9 of the largest representative United States installations, the depth from the flow line to the slot varies from 10 feet 10 inches to 13 feet 6 inches. Imhoff states, concerning the depth of tanks: Deep tanks are to be preferred to shallow tanks because in them the decomposition of the sludge is improved. This is so because in the deeper tanks the temperature is maintained more uniformly and because the stirring action of the rising gas bubbles is more intense. The stirring action of the gas bubbles is desirable as it brings the fresh sludge more quickly under the influence of the active bac- terial agents. The greater pressure on the sludge in deep tanks also reduces its moisture content. Two or more sedimentation chambers are sometimes used over one sludge digestion chamber in order to avoid the depths called for by the sloping sides of a single sedimentation chamber. An objection to multiple-flow chambers is the possibility of interchange of liquid from one chamber to another through the common digestion chamber. The inlet and outlet devices should be so constructed that the direction of flow in the tank can be reversed in order that the accumulated sludge may be more evenly distributed in the hop- pers of the digestion chamber. The sewage should leave the sedimentation chamber over a broad crested weir in order to minimize fluctuations in the level of sewage in the tank. The gases in the digesting sludge are sensitive to slight changes in pressure. A lowering of the level of sewage will release com- pressed gas and will too violently disturb the sludge in the digestion chamber. Hanging baffles, submerged 12 to 16 inches and projecting 12 inches above the surface of the sewage, should be placed in front of the inlet and outlet, and in long tanks inter- mediate baffles should be placed to prevent the movement of 1 Municipal Engineering, Vol. 54, p. 149. 422 SEPTICIZATION scum or its escape into the effluent. An Imhoff tank which is operating properly should not have any scum on the surface of the sewage in the sedimentation chamber. The slot or opening at the bottom of the sedimentation chamber should not be less than 6 inches wide between the lips. Wider slots are preferable, but too wide a slot will involve too much loss of volume in the digestion chamber. One lip of the slot should project at least 3 inches horizontally under the other so as to prevent the return of gases through the sedimentation chamber. A triangular beam may be used as shown in Fig. 161 A. This method of construction is advantageous in increasing the available capacity for sludge storage. The digestion chamber should be designed to store sludge from 6 to 12 months, the longer storage periods being used for smaller installations. In warm climates a shorter period may be used with success. The amount of sludge that will be accumulated is as uncertain as in other forms of sewage treatment. A widely quoted empirical formula, presented in " Sewage Sludge " by Allen, states: C = 10 . 5 P D for combined sewage; C = 5 . 25 P D for separate sewage, in which C = the effective capacity of the digestion chamber in cubic feet; P=the population served, expressed in thousands; D = the number of days of storage of sludge. The effective capacity of the chamber is measured as the entire volume of the chamber approximately 18 inches below the lower lip of the slot. The capacity as computed from the above formula is assumed as satisfactory for a deep tank. Frank and Fries 1 recommend the increase of the capacity for shallow tanks to compensate for the decreased hydrostatic pressure. In any event the formula can be no more than a guide to design. No formula can be of equal value to data accumulated from tests on the sewage to be treated. The Illinois State Board of Health requires 3 cubic yards of sludge digestion space per million gallons of sewage treated. Frank and Fries recommend an allowance of 0.007 cubic foot of storage per inhabitant per day for combined sewage and one-half that amount for separate 1 Eng. Record, Vol. 68, 1913, p. 452. DESIGN OF IMHOFF TANKS 423 sewage. If this is based on 80 per cent moisture content, the volume for other percentages of moisture can be easily com- puted. An average figure used in the Emscher District is one cubic foot capacity for each inhabitant for the combined system, and three-fourths of this for the separate system. Metcalf and Eddy 1 recommend the following method for the deter- mination of the sludge storage capacity: (1) From analyses of the sewage or study of the sources ascertain the amount of sus- pended matter. (2) Assume, or determine by test, the amount which will settle in the period of detention selected, say 60 per cent in 3 hours. (3) Estimate the amount which will be digested in the sludge chamber at about 25 per cent, leaving 75 per cent to be stored. (4) Estimate the percentage moisture in the sludge conservatively, say 85 per cent. The total volume of sludge can then be computed. This method is more rational than the use of empirical formulas, but because of the estimates which must be made its results will probably be of no greater accuracy than those obtained empirically. The digestion chamber is made in the form of an inverted cone or pyramid with side slopes at most about 2 horizontal to 1 vertical and preferably much steeper without necessitating too great a depth of tank. The purpose of the steep slope is to con- centrate the sludge at the bottom of the hopper thus formed. Concrete is ordinarily used as the material of construction as a smooth surface can be obtained by proper workmanship. Where flat slopes have been used, a water pipe perforated at intervals of 6 to 12 inches may be placed at the top of the slopes, and water admitted for a short time to move the sludge when the tank is being cleaned. A cast-iron pipe, 6 to 8 inches in diameter, is supported in an approximately vertical position with its open lower end supported about 12 inches above the lowest point in the digestion chamber. This is used for the removal of sludge. A straight pipe from the bottom of the tank to a free opening in the atmosphere is desir- able in order to allow the cleaning of the pipe or the loosening of sludge at the start, and to prevent the accumulation of gas pockets. The sludge is led off through an approximately hori- zontal branch so located that from 4 to 6 feet of head are available for the discharge of the sludge. A valve is placed on the hori- 1 Am. Sewerage Practice, Vol. Ill, p. 437. 424 SEPTICIZATION zontal section of the pipe. A sludge pipe is shown in Fig. 162 and 163. Under such conditions, when the sludge valve is opened the sludge should flow freely. The hydraulic slope to insure proper sludge flow should not be less than 12 to 16 per cent. Where it is not possible to remove the sludge by gravity an air lift is the best method of raising it. The volume of the transition or scum chamber should equal about one-half that of the digestion chamber. The surface area of the scum chamber exposed to the atmosphere should be 25 to 30 per cent of the horizontal projection of the top of the digestion chamber. Some tanks have operated successfully with only 10 per cent, but troubles from foaming can usually be anticipated unless ample area for the escape of gases has been provided. All portions of the surface of the tank should be made accessible in order that scum and floating objects can be broken up or removed. The gas vents should be made large enough so that access can be gained to the sludge chamber through them when the tank is empty. Precautions should be taken against the wrecking of the tank by high ground water when the tank is emptied. With an empty tank and high ground water there is a tendency for the tank to float. The flotation of the tank may be prevented by building the tank of massive concrete with a heavy concrete roof, by underdraining the foundation, or by the installation of valves which will open inwards when the ground water is higher than the sewage in the tank. Dependence should not be placed on the attendant to keep the tank full during periods of high ground water. Roofs are not essential to the successful operation of Imhoff tanks. They are sometimes used, however, as for septic tanks, to assist in controlling the dissemination of odors, to minimize the tendency of the sewage to freeze, and to aid in bacterial activity. In the construction of a roof, ventilation must be provided as well as ready access to the tank for inspection, cleaning, and repairs. 251. Imhoff Tank Results. The Imhoff tank has the advantage over the septic tank that it will not deliver sludge in the effluent, except under unusual conditions. The Imhoff tank serves to digest sludge better than a septic tank and it STATUS OF IMHOFF TANKS 425 will deliver a fresher effluent than a plain sedimentation tank. Imhoff sludge is more easily dried and disposed of than the sludge from either a septic or a sedimentation tank. This is because it has been more thoroughly humified and contains only about 80 per cent of moisture. As it comes from the tank it is almost black, flows freely and is filled with small bubbles of gas which expand on the release of pressure from the bottom of the tank, thus giving the sludge a porous, sponge-like consist- ency which aids in drying. When dry it has a inoffensive odor like garden soil, and it can be used for filling waste land, without further putrefaction. It has not been used successfully as a fertilizer. Offensive odors are occasionally given off by Imhoff tanks, even when properly operated. They also have a tendency to " boil " or foam. The boiling may be quite violent, forcing scum over the top of the transition chamber and sludge through the slot in the sedimentation chamber, thus injuring the quality of the effluent. The scum on the surface of the transition chamber may become so thick or so solidly frozen as to prevent the escape of gas with the result that sludge may be driven into the sedi- mentation chamber. Some chemical analyses of Imhoff tank influents and efflu- ents are given in Table 86 and the analyses of some sludges from Imhoff tanks are given in Table 83. It is to be noted that the nitrites and nitrates are still present in the effluent, whereas they are seldom present in the effluent from septic tanks. The per cent of moisture in the Imhoff sludge is less than that in the septic tank sludge, and its specific gravity is higher. It is heavier and more compact because of the longer time and the greater pressure it has been subjected to in the digestion chamber of the Imhoff tank. 252. Status of Imhoff Tanks. The introduction of the Imhoff tank into the United States, like the introduction of the Burkli-Ziegler Run-Off Formula, and Kutter's Formula, is to be credited to Dr. Rudolph Hering. He advised Dr. Imhoff to come to the United States to introduce his tank and gave him material aid through recommendations and introductions to engineers. Shortly after its introduction, in 1907, the tank became very popular and installations were made in many cities. This popularity was caused by a growing dissatisfaction 426 SEPTICIZATION with the septic tank, the litigation then progressing over septic patents, the production of inoffensive sludge, and the promising results which had been obtained in Germany. As a result of the extended experience obtained in the use of Imhoff tanks American engineers have learned that, like all other sewage treatment devices introduced up to the present time, the Imhoff tank requires experienced attention for its successful operation. These tanks are now being installed in the place of septic tanks, and they are frequently used in conjunction with sprinkling filters. 253. Operation of Imhoff Tanks. The important feature in the successful operation of an Imhoflf tank is the proper control of the sludge and transition chambers. During the ripening process, which may occupy 2 weeks to 3 months after the start of the tank, offensive odors may be given off, the tank may foam violently, and scum may boil over into the sedi- mentation chamber. This is usually due to an acid condition in the digestion chamber which may possibly be overcome by the addition of lime. A very fresh influent will have a similar effect. Too violent boiling is not likely to occur where the area for the escape of gas has been made large and the gas is not confined. Any accumulation of scum should be broken up and pushed down into the digestion chamber, or removed from the tank. The stream from a fire hose is useful in breaking up scum. The side walls of the sedimentation chamber should be squeegeed as frequently as is necessary to keep them free from sludge, which may be as often as once or twice a week. Material floating on the surface of the sedimentation chamber should be removed from the tank or sunk into the digestion chamber through the gas vents in the transition chamber. No sludge should be removed, except for the taking of samples, until the tank is well ripened. The ripening of the sludge can be determined by examining a sample and observing its color and odor. An odorless, black, granular, well humified sludge is indicative of a ripened tank. After the tank has ripened, sludge should be removed in small quantities at 2 to 3-week intervals, except in cold or rainy weather. The sludge should be drawn off slowly to insure the removal of the oldest sludge at the bottom of the digestion chamber. After the drawing off of the sludge has ceased the pipe should be flushed with fresh water to prevent its clogging with dried sludge in the interim until the next OTHER TANKS 427 removal. Under no circumstances should all the sludge in the tank be removed at any time. The removal of some sludge during foaming after ripening may reduce or stop the foaming. The ripening of a tank can be hastened by adding some sludge from a tank already ripened. Sludge should not be allowed to accumulate within 18 inches of the slot at the bottom of the digestion chamber. The elevation of the surface of the sludge can be located by lowering into the tank, a stoppered, wide-mouthed bottle on the end of a stick. The stopper is pulled out by a string when the bottle is at some known elevation. The bottle is then carefully raised and observed for the presence of sludge. The process is repeated with the bottle at different elevations until the surface of the sludge has been discovered. Another method is to place the suction pipe of a small hand pump at known points, successively increasing in depth, and to pump in each position until one posi- tion is found at which sludge appears in the pump. When the sludge in one portion of the digestion chamber has risen higher than in another portion, the direction of flow in the sedimentation chamber should be reversed if possible. In the ordinary routine of operation it is never necessary to shut down an Imhoff tank. Sludge is removed while the tank is operating. The shut down of a tank will be caused by accidents and breaks to the structure or control devices. 254. Other Tanks. The Travis Hydrolytic Tank represents a step in the development from the septic tank to the Imhoff tank. The Doten tank and the Alvord tank are recent develop- ments, and are somewhat similar in operation to the Imhoff tank. The Travis Hydrolytic Tank when first designed differed from the later design of the Imhoff tank in the slot between the sedimentation chamber and the digestion chamber which was not trapped against the escape of gas from the latter to the former, and in operation a small quantity of fresh sewage was allowed to flow through the digestion chamber. The tank is called a hydrolytic tank because some solids are liquefied in it. The tank is mainly of historic interest as designs similar to it are rarely made to-day. Better results are obtained from the use of the Imhoff tank. Recent developments have altered the original design of the Travis tank so that it is hardly recognizable. 428 SEPTICIZATION The Travis tank at Luton, Eng., is shown in Fig. 164. The detailed description given in the Engineering News in connection with this illustration shows that the governing object of the design is to separate as quickly as possible the sludge deposited HYDROLIZING CHAMBER-. **X J&- sl8"0utle+ Carrier fo Pilfer Beds ,9 "In let FIG. 164. Plan and Section of Hydrolytic Tank at Luton, England. Eng. News, Vol. 76, 1916, p. 194. by the sewage without septic action being set up. To aid in the collection and settlement of flocculent matter vertical wooden grids or colloiders are used. The suspended matter strikes these and forms a slimy deposit on them that in a short time slips off in pieces large enough to settle readily. OTHER TANKS 429 The Doten tank 1 is a single-storied, hopper-bottomed septic tank, views of which are shown in Fig. 165. It was devised by L. S. Doten for army cantonments during the War. Its chief purpose was to avoid the foaming and frothing so common to Imhoff tanks when overdosed with fresh sewage. The first Alvord tank was constructed in Madison, Wis., in 1913. 2 As now constructed the tank consists of three deep, single-story com- partments with hopper bottoms. These compartments are arranged side by side in any one unit. Sewage enters at the sur- < Slope 1.4% 8 "C.I. Soil Pipe, kludge Drctfn^ K- 10 "Gatevalve %<-8 "6ate Valves - _- 4- 0*4-0 "trap Doors , Slope Gutter to End of Building Trap . . , | Doors -Q 97 9 "~ tzr - 23-6- *i,|c 23-6 ->!,!< ?3- 'V5- '-/ K - 8 "Gate Valve X, &heafh-,6*6" ing-, Plan of Septic Tank Section B-B FIG. 165. Doten Tank for Army Cantonment Sewage Disposal. Eng. News-Record, Vol. 79, 1917, p. 931. face of one of the compartments and is retained here during one-half of the total period of retention. It leaves the first compartment over a weir and passes in a channel over the top of the intermediate compartment to the third or effluent com- partment, where it is held for the remainder of the period of detention. Accumulated scum and sludge are drawn off into the intermediate compartment at the will of the operator, this 1 Trans. Am. Society Civil Engineers, Vol. 83, 1920, p. 337. 2 Eng. News Record, Vol. 83, 1919, p. 510. 430 SEPTICIZATION compartment being used for sludge digestion only. Such tanks as the Doten and the Alvord have been used for plants receiving .very fresh sewages such as is discharged from military canton- ments, in order to assist in the prevention of the foaming to be expected from an Imhoff tank receiving such a fresh influent. The tanks are suitable for small installations, or where excavation to the depth required for an Imhoff tank is not practicable. CHAPTER XVII FILTRATION AND IRRIGATION 255. Theory. The cycle through which the elements forming organic matter pass from life to death and back to life again has been described in Chapter XIII. It has been shown in Chapter XVI that septic action occupies that portion of the cycle in which the combinations of these elements are broken down or reduced to simpler forms and the lower stages of the cycle are reached. The action in the filtration of sewage builds up the compounds again in a more stable form and almost complete oxidation is attained, dependent on the thoroughness of the filtration. In the filtration of sewage only the coarsest particles of suspended matter are removed by mechanical straining. The success of the nitration is dependent on biologic action. The desirable form of life in a filter is the so-called nitrifying bacteria which live in the interstices of the filter bed and feed upon the organic matter in the sewage. Anything which injures the growth of these bacteria injures the action of the filter. In a properly constructed and operated filter, all matter which enters in the influent, leaves with the effluent, but in a different molec- ular form. A slight amount may be lost by evaporation and gasification but this is more than made up by the nitrogen and oxygen absorbed from the atmosphere. The nitrifying action in sewage filtration is shown by the analysis of sewage passing through a trickling filter, as given in Tables 86 and 87. It is shown by the reduction of the content of organic nitrogen, free ammonia, oxygen consumed, and the increase in nitrites, nitrates, and dissolved oxygen. The reduction of suspended matter is interrupted periodically when the filter " unloads." The sus- pended matter in the effluent is then greater than in the influent. The nitrifying organisms have been isolated and divided into two groups nitrosomonas, the nitrite formers, and nitrcbader, the nitrate formers. Experiments indicate that the growth of the 431 432 FILTRATION AND IRRIGATION nitrobacter organisms is dependent on the presence of the nitrosomonas organisms, which are in turn dependent on the presence of the putrefactive compounds resulting from the action of putrefying bacteria. The existence of these organisms is an example of symbiotic action in bacterial growth. The organisms have been found to grow best on rough porous material on which their zoogleal jelly can be easily deposited and affixed. Sewage filters were constructed to provide these ideal conditions before the action of a filter was thoroughly understood. The action in irrigation is similar to that in filtration. Although more strictly a method of final disposal rather than preliminary treatment, the similarity of the actions which take place, and the grading of sand filtration into broad irrigation with no distinct line of difference has resulted in the inclusion of the discussion of irrigation in the same chapter with filtration. 256. The Contact Bed. A contact bed is a water-tight basin filled with coarse material, such as broken stone, with which sewage and air are alternately placed in contact in such a manner that oxidation of the sewage is effected. A contact bed has some of the features of a sedimentation tank and an oxidizing filter. As such it marks a transitory step from anaerobic to aerobic .treatment of sewage. A plan and a section of a contact bed are shown in Fig. 166. Because of its dependence on biologic action a contact bed must be ripened before a good effluent can be obtained. The ripening or maturing occurs progressively during the first few weeks of operation, the earlier stages being more rapidly developed. The time required to reach such a stage of maturity that a good effluent will be developed will vary between one and six or eight weeks, dependent on the weather and the character of the influent. During the period of maturing the load on the bed should be made light. The use of contact beds has been extensive where a more stable effluent than could be obtained from tank treatment has been desired, yet the best quality of effluent was not required. The sewage to undergo treatment in a contact bed should be given a preliminary treatment to remove coarse suspended matter. The efficiency of the contact treatment can be increased by passing the sewage through two or three contact beds in series. In double contact treatment the primary beds are filled with THE CONTACT BED 433 coarser material and operate at a more rapid rate than the secondary beds. Double contact gives better results than single contact, but triple-contact treatment, though showing excellent results, is hardly worth the extra cost. An advantage which contact treatment has over all other methods of sewage filtration is that the bed can be so operated that the sewage is never exposed to view. As a result the odors from well-operated contact beds are slight or are entirely absent and there should be Sand Filters 151' Contact , Beds 148- Jior. Scale. 20' 40' 60' m. A A I \JopofWal\, \EI.1123 \^-^ _1 __'".. \ ':% I Top of Wall, \EIX73 p 4rh^lr"^^-'*^^- -* f 9^PRWP > ""TopofSond.EI.3lM , t Longitudinal Section. FIG. 166. Plan and Section of Treatment Plant at Marion, Ohio, Showing Septic Tank, Contact Bed, and Sand Filter. 1908 Report Ohio State Board of Health. no trouble from flying insects. Such a method of treatment is favorable to plants located in populous districts and to the fancies of a landscape architect. Another advantage of the contact bed is the small amount of head required for its operation, which may be as low as 4 to 5 feet. This low head consumption by a sewage filter is equaled only by the intermittent sand filter. The quality of the effluent from some contact beds is shown in Table 85. It is to be noted that nitrification has been carried to a fair degree of completion, and that the reduction of oxygen consumed has been marked. In comparison with the effluent 434 FILTRATION AND IRRIGATION from filters, contact effluent contains a smaller amount of nitro- gen as nitrites and nitrates, and suspended solids. Contact effluent is usually clear and odorless, but it is not stable without dilution. The absence of nitrites and nitrates is sometimes advantageous as the effluent will not support vegetable growths dependent on this form of nitrogen. The absence of suspended solids obviates the use of secondary sedimentation basins which are needed with trickling 'filters. The head of 5 to 8 feet required for contact treatment is law in comparison to the 10 to 15 feet required for trickling filters, but is slightly higher than the head required for intermittent sand filtration. The cost of contact treatment is higher than the cost of trickling filters but is lower than the cost of intermittent sand filtration, as shown in Table 90. TABLE 85 QUALITY OF EFFLUENTS FROM CONTACT BEDS Report on Sewage Purification at Columbus, Ohio, by G. A. Johnson, 1905. 1 Nitrogen as Suspended Matter ^i m Size of Rate, Million I 08 I Material Gallons o '3 T-I HH in Inches per Acre H 55 | a $ 0) 1 h g per Day 1 '3 Q Q OS 3 ^ 3 a H 8-S 'C h 3 J5 8 ra a) Q X O 1 '1 1 6 o i Q Parts per Million A 5 0.25-1.00 0.953 23 3.5 8.7 0.20 1.6 832 94 737 0.3 B 5 0.25-2.00 1.514 21 4.0 8.4 0.15 1.4 831 85 746 0.1 C 5 0.25-1.50 1.222 24 3.5 10.8 0.11 0.6 826 92 734 0.8 D 5 0.50-1.50 1.405 22 3.3 9.5 0.13 0.9 810 91 717 0.9 Per Cent Removal of Constituer its of Appli< ;d Sew age A 5 0.25-1.00 0.953 48 49 10 73 70 76 . 25-2 . 00 1.514 52 40 11 80 77 83 c 5 0.25-1.50 1.222 47 31 12 70 70 70 D 5 0.50-1.50 1.405 46 37 19 67 61 72 The depth of the contact bed is generally made from '4 to 6 feet. The deeper beds are less expensive per unit of volume, to construct, as the cost of the under drains and the distribution system is reduced in relation to the capacity of the filter. The increased depth reduces the aeration, and the periods of filling THE CONTACT BED 435 and emptying are so increased as to limit the depths to the figures stated. The other dimensions of the bed are controlled by economy and local conditions, as the success of the contact treatment is not affected by the shape of the bed. Contact units are seldom constructed larger than one-half an acre in area, as larger beds require too much time for filling and emptying. A large number of small units is also undesirable because of the increased difficulty of control. In general it is well to build as large units as are compatible with efficient operation, elasticity of plant, and which can be filled within the time allowed at the average rate of sewage flow, or from dosing tanks in which the storage period is not so long as to produce septic conditions. The interstices in a contact bed will gradually fill up, due to the deposition of solid matter on the contact material, the dis- integration of the material, and the presence of organic growths. The period of rest allowed every five or six weeks tends to restore partially some of this lost capacity through the drying of the organic growths. It is occasionally necessary to remove the material from the bed and wash it in order to restore the original capacity. It may be necessary to do this three or four times a year, in an overloaded plant, or as infrequently as once in five or six years in a more lightly loaded bed. The period is also dependent on the character of the contact material and the quality of the influent. This loss of capacity may reduce the voids from an original amount of 40 to 50 per cent of voids to 10 to 15 per cent. If the bed is not overloaded the loss of capacity will not increase beyond these figures. The rate of filtration depends on the strength of the sewage, the character of the contact material, and the required effluent. It should be determined for any particular plant as the result of a series of tests. For the purposes of estimation and com- parison the approximate rate of filtration should be taken at about 94 gallons per cubic yard of filtering material per day on the basis of three complete fillings and emptyings of the tank. This is equivalent to 150,000 gallons per acre foot of depth per day, or for a bed 5 feet deep to a rate of 750,000 gallons per acre per day. The net rate for double or triple filtration is less than these figures, but on each filter the rates are higher. The material of the contact bed should be hard, rough, and angular. It should be as fine as possible without causing clogging 436 FILTRATION AND IRRIGATION of the bed. Materials in successful use are: crushed trap rock or other hard stone, broken bricks, slag, coal, etc. Soft crumbling materials such as coke are not suitable as the weight of the superimposed material and the movement of the sewage crushes and breaks it into fine particles which accumulate in the lower portion of the filter and clog it. Roughness, porosity, and small size are desirable, as the greater the surface area the more rapid the deposition of material. After a short time, however, the advantages of roughness and porosity are lost, as the sediment soon covers all unevenness alike. The minimum size of the material is limited by the tendency towards clogging. The sizes in successful use vary between J and j of an inch, J inch being a common size. The same size of material is used throughout the depth of the bed except that the upper 6 inches may be composed of small white pebbles or other clean material, which does not come in contact with the sewage and which will give an attractive appearance to the plant. In double or triple con- tact beds 3 or 4-inch material is sometimes used for the primary beds, and J-inch material in the final bed. Sewage may be applied at any point on or below the surface. The sewage is withdrawn from the bottom of the bed. It is undesirable to have too few inlet or outlet openings as the velocity of flow about the openings will be so great as to disturb the deposit on the contact material. The distribution system and the underdrains for the bed at Marion, Ohio, are shown in Fig. 166. The cycle of operation of a contact bed is divided into four periods. A representative cycle might be: time of filling, one hour; standing full, 2 hours; emptying, one hour; standing empty, 4 hours. The length of these periods is the result of long experience based on many tests and are an average of the conclu- sions reached. Wide variations from them may be found in different plants, and tests may show successful results with different periods. The combination of these four periods is known as the contact cycle. The period of filling should be made as short as possible without disturbing the material of the bed nor washing off the accumulated deposits. The sewage should not rise more rapidly than one vertical foot per minute. During the contact or stand- ing full period sedimentation and adsorption of the colloids are THE TRICKLING FILTER 437 occurring on the area of surface exposed to the sewage. This period should be of such length that septic action does not become pronounced, and long enough to permit of thorough sedimenta- tion. The period of emptying should be made as short as possible without disturbing the bed, on the same basis that the period of filling is determined. During the period of standing empty, air is in contact with the sediment deposited in thin layers on the contact material, and the oxidizing activities of the filter are taking place. The filter is given a rest period of one or two days every five or six weeks, in order that it may increase its capacity and it biologic activity. The control of a contact bed may be either by hand or auto- matic, the latter being the more common. Hand control requires the constant attention of an operator and results in irregularity of operation, whereas automatic control will require inspection not more than once a day and insures regularity of operation. A number of automatic devices have been invented which give more or less satisfaction. The air-locked automatic siphons, without moving parts, have proven satisfactory and are practi- cally " fool-proof." The operation of these devices is explained in Chapter XXI. 257. The Trickling Filter. A trickling or sprinkling filter is a bed of coarse, rough, hard material over which sewage is sprayed or otherwise distributed and allowed to trickle slowly through the filter in contact with the atmosphere. A general view of a trickling filter in operation at Baltimore is shown in Fig. 167. The action of the trickling filter is due to oxidation by organisms attached to the material of the filter. The solid organic matter of the sewage deposited on the surface of the material, is worked over and oxidized by the aerobic bacteria, and is discharged in the effluent in a more highly nitrified con- dition. At times the discharge of suspended matter becomes so great that the filter is said to be unloading. The action differs from that in a contact bed in that there is no period of septic or anaerobic action and the filter never stands full of sewage. The effluent from a trickling filter is dark, odorless, and is ordinarily non-put rescible. Analyses of typical effluents are given in Tables 86 and 87. The unloading of the filter may occur at any time, but is most likely to occur in the spring or in a warm period following a period of low temperatures. It causes 438 FILTRATION AND IRRIGATION higher suspended matter in the effluent than in the influent and may render the effluent putrescible. The action is marked by the discharge of solid matter which has sloughed off of the filter material and which increases the turbidity of the effluent. Where the diluting water is insufficient to care for the solids so carried in the effluent, they can be removed by a 2-hour period of sedimentation. The effluent may become septic during this time, however. The nitrogen in the effluent is almost entirely in the form of nitrates, and the percentage of saturation with dissolved oxygen is high. The effluent is more highly nitrified than that from a contact bed, and its relative stability is also higher, thus demanding a smaller volume of diluting water. FIG, 167. Sprinkling Filter in Operation in Winter at Baltimore. The principal advantage of a trickling filter over other methods of treatment is its high rate which is from two to four times faster than a contact bed, and about seventy times faster than an inter- mittent sand filter. The greatest disadvantage is the head of 12 to 15 feet or more necessary for its operation. Sedimentation of the effluent is usually necessary to remove the settleable solids. During the period of secondary sedimentation the quality of the filter effluent may deteriorate in relative stability. In winter the formation of ice on the filter results in an effluent of inferior quality, but as the diluting water can care for such an effluent at this time the condition is not detrimental to the use of the trickling filter. In summer the filters sometimes give off offen- sive odors that can be noticed at a distance of half a mile, and flying insects may breed in the filter in sufficient quantities to THE TRICKLING FILTER 439 become a nuisance if preventive steps are not taken. The dis- semination of odors is especially marked when treating a stale or septic sewage. The treatment of a fresh sewage seldom results in the creation of offensive odors. TABLE 86 ANALYSIS OF CRUDE SEWAGE, IMHOFF TANK, AND SPRINKLING FILTER EFFLUENTS AT ATLANTA, GEORGIA (Engineering Record, Vol. 72, p. 4) Temperature Fahrenheit Parts per Million Cent Saturation, dissolved Oxygen ative Stability Nitrogen as Oxygen Con- sumed Suspended Matter Organic Free Am- monia | Nitrates "(3 .2 eS 1 1 Crude Se-mage 1913 Maximum 77 15.6 21.8 0.1 3.0 100.0 371 154 163 47 Minimum 61 10.4 16.5 0.1 1.4 78.3 222 98 112 11 Average 70 12.8 18.8 0.1 2.2 90.6 285 126 138 28 1914 (7 months) Maximum .... 74 16.9 33.4 2.3 431 48 .Minimum . 60 9.5 18.1 1.6 279 12 Average 66 13.4 27.1 2.0 351 30 Imhoff Effluent 1913 Maximum 78 13.2 21.9 0.2 3.1 68.0 90 50 41 Minimum 58 6.5 16.8 0.1 1.1 53.1 35 42 21 Average 68 9.0 20.0 0.2 2.1 60.1 68 46 33 1914 (7 months) Maximum ..... 77 10.3 30.3 2.0 73 48 Minimum 59 4.1 18.0 1.5 49 34 Average 65 7.7 25.9 1.8 65 43 Sprinkling Filter Effluent 1913 Maximum 79 5.6 14.2 0.8 11.3 32.1 60 31 28 76 99 Minimum 55 2.6 6.2 0.5 5.8 23.6 33 26 28 52 88 Average 66 3.8 9.9 0.7 8.2 28.2 49 28 28 64 89 1914 (7 months) Maximum 77 8.5 20.7 11.2 106 79 99 Minimum 55 4.4 8.8 3.6 40 55 89 Average 63 5.7 15.2 7.2 62 65 95 440 FILTRATION AND IRRIGATION 3 9 I S | Oxygen Consumed Organic Nitrogen UOT 11 T JA[ OOO^- CDlClt- i-l O Tji CQ eo cc t^ 8 8 J8d S^JBJ (N ^ iO CC -HOOO COt^OOCO * Tti.co cc OO5COC v'Flushmq Gallery = : i 1 6 "C. i. Wafer Mam^ ^ 6 "Disch. Pipe Grade 0.0028'' ; ^30"By-Hass 30 Concrete Drain Conduit- Plan FIG. 168. Section through Sprinkling Filter at Fitchburg, Mass., Showing Distribution System. Eng. Record, Vol. 67, p. 634. of the control house, but it does not always lend itself favorably 'to the local conditions, and the piping and nozzle location are not so simple. The gridiron system lends itself favorably to the equalization of head losses. The pipes used should be larger than would be demanded by considerations of economy alone, both for the purpose of reduction of head loss and ease in cleaning. No pipe less than 6 inches in diameter should be used, and the average velocity of flow should not exceed one foot per second. Cast iron, concrete, or vitrified clay pipe may be used, but cast 444 FILTRATION AND IRRIGATION iron is the material commonly used. The system should be arranged for easy flushing and cleaning and the pipes so sloped that the entire system can be drained in case of a shut down in cold weather. The pipes are placed far enough below the surface of the filling material so that the top of the spraying nozzle is 6 to 12 inches above the surface of the filter. If the pipes are placed near the surface they are accessible for repairs, but are exposed to temperature changes. If the pipes are large their presence near the surface of the filter may seriously affect the distribution of the sewage through the filter. If the distributing pipes are placed near the bottom of the filter they are inaccessible for repairs and the nozzles must be connected to them by means of long riser pipes. The distributing pipes should be supported by columns extending to the foundation of the filter bed, there being a column at every pipe joint with such intermediate sup- ports as may be required. In some plants the pipes have been supported by the filtering material. Although slightly less expensive in first cost the practice of so supporting the pipes is poor, as settling of the material may break the pipe or cause leaks, and if the bed becomes clogged, removal of the material is made more difficult. Valves should be placed in the distribut- ing system in such a manner that different sets of nozzles can be cut out at will, thus resting those portions of the filter and permitting repairs without shutting down the entire filter. The spacing of the nozzles is fixed by the type and size of the nozzle, the available head, and the rate of filtration. Various types of sprinkler nozzles are shown in Fig. 169 and the dis- charge rates, head losses, and distances to which sewage is thrown for the Taylor nozzles, are shown in Fig. 170. Nozzles are available which will throw circular, square, or semicircular sprays. In the use of circular sprays there is necessarily some portion of the filter which is underdosed if the nozzles are placed at the corners of squares with the sprays tangent, and there is an overdosing of other portions if the sprays are allowed to overlap so that no portion of the filter is left without a dose. Rectangular sprays will apparently overcome these difficulties, but studies have shown that circular sprays with some over- lapping, and the nozzles placed at the apexes of equilateral tri- THE TRICKLING FILTER 445 i. hase Square Nozzle A= Diameter of Orifice. Diameter of Spindle at Orifice. Priestman-Beddoes Weand, Atlantic Type Round Nozzle. Round Nozzle. Worcester' Round FIG. 169. Sprinkling Filter Nozzles. Bulletin No. 3, Engineering Experiment Station, Purdue University. Discharge, Gallons per Min-ute 30 28 26 24 22 20 18 16 14 12 10 10 12 14 16 Nozzle Spacing, Feet., 20 FIG. 170. Diagram Showing the Discharge and Spacing of Taylor Nozzles. 446 FILTRATION AND IRRIGATION angles as shown in Fig. 172 will give as satisfactory distribution as other forms. The nozzles should be selected to give the best distribution, to consume all of the head available, and to give the proper cycle of operation. The entire head available should be consumed in order that the fewest number of nozzles may be used. An excellent study of the characteristics of various types of nozzles has been published in Bulletin No. 3 of the Engineering Experi- ment Station at Purdue University, 1920. As a result of the tests on the nozzles shown in Fig. 169, it was determined for all nozzles, except No. 8, that in which Q =the rate of discharge in cubic feet per second; C =a coefficient shown in Table 88; a=the net cross-sectional opening of the nozzle in square feet; h =the pressure on the nozzle in feet of water. TABLE 88 COEFFICIENTS OF DISCHARGE FOR SPRINKLER NOZZLES SHOWN IN FIG. 169 Nozzle Number 1 2 3 4 5 6 7 Coefficient 648 756 696 666 675 598 569 It is evident that if the head on the nozzles is constant and the nozzle throws a circular spray, the intensity of dosing at the circumference will be greater than nearer the center. This difficulty is overcome by so designing the dosing tank from which the sewage is fed that the head on the nozzle and the quantity thrown will vary in such a manner that the distribution over the bed is equalized. Intermittent action is obtained by an automatic siphon which commences to discharge when the tank is full and empties the tank in the period allowed for dosing. Under such conditions the tank should discharge for a longer time at the higher heads than at the lower heads as there is more territory to be covered at the higher heads. The design of the tank to do this with exactness is difficult, and the con- struction of the necessary curved surfaces is expensive. Where THE TRICKLING FILTER 447 a dosing tank is used for such conditions it has been found satis- factory to construct the tank with plane sides sloping at approxi- mately 45 degrees from the vertical (or horizontal). A tank with curved surfaces is shown in Fig. 171. The dosing siphon is usually placed in the tank as shown in the figure. The head and quantity of discharge through the nozzles can be varied also by maintaining a constant depth in a dosing tank by means <-iz- f> % />-*> V4 7>a:.\>". : 3'- v/ Elevation of Sprinkler Nozzle FIG. 171. Section of 12-inch Siphon and Dosing Tank, for King's Park, Island. Long of a float feed valve, and varying the head and quantity dis- charged to the nozzles by a butterfly valve in the main feed line, or by the use of a Taylor undulating valve designed for this purpose. The butterfly valve is opened and closed by a cam so designed and driven at such a rate that the required distribu- tion is obtained. The Taylor undulating valve is opened and closed at a constant rate, the shape of the valve giving the required variations in head and discharge Other methods of control have been attempted but have not been used exten- sively. An example of the design of the nozzle layout and dosing tank for a sprinkling filter follows : 448 FILTRATION AND IRRIGATION Let it be required to determine the nozzle layout for one acre of sprinkling filters with 5 feet available head on the nozzles. The selection of the type of nozzle and the size of opening is a matter of judgment and experience. Noz- zles with large openings are less liable to clog and fewer nozzles are needed than where small nozzles are used, but the distribution of sewage is not so even as with the use of small nozzles. In this example Taylor circular spray nozzles will be selected. Fig. 170 shows that a Taylor circular spray nozzle will discharge 22.3 g.p.m. under a head of 5 feet, and that the economical nozzle spacing will be 15.3 feet. The least number of nozzles at this spacing required for a bed of one acre in area is found as follows: In Fig. 172, let n equal the number of FIG. 172. Typical Sprinkler Nozzle Layout. nozzles in a horizontal row, counting half -spray nozzles as J, and let ra equal the number of rows counting rows of half- spray nozzles as half rows. 1 Then the number of nozzles, N, equals mn, and 15.3wXl3.2n equals 43,560 or mn equals 215. The next step should be the design of the dosing tank and siphon. It is possible to design a tank which will give equal distribution over equal areas of filter surface. It has been 1 The use of half-spray nozzles is not always advocated as it is consid- ered that their use does not markedly improve the distribution. Where half nozzles are used, a margin of 18 inches to 2 feet should be allowed between the edge of the filter and the nozzle, to prevent the blowing of raw sewage from the filter. THE TRICKLING FILTER 449 found, however, that the expense of this refinement is unwar- ranted as there are a number of outside factors which tend to overcome the theoretical design. The effect of wind, unequal spacing, and irregularities in the elevation of the nozzles have a tendency to offset refinements in the design of a dosing tank. It is therefore the general practice to slope the sides of the tank at an angle of about 45 degrees as previously stated. The dosing tank is generally designed to have a capacity which will give a complete cycle of operation once in 15 minutes. In the ordinary design the factors given are the rate of inflow and the given time of filling. In the following example the time of filling will be taken as 10 minutes, the time of emptying as 5 minutes, and the rate of flow as 1,000,000 gallons per day. The capacity 1 000 000 of the tank will therefore be ' ' =7,000 gallons. The diameter of the siphon to be selected can be computed as follows : Let Q =the capacity of the tank in cubic feet; qi = the rate of discharge of the siphon in cubic feet per second ; #2 = the rate of inflow to the tank in cubic feet per second ; q = the rate of emptying the tank in cubic feet per second = (tfi-22); A =the cross-sectional area of the free surface of the water in the tank at any instant, in square feet; a = the cross-sectional area of the siphon in square feet ; b = the small dimension of the base of the tank in feet ; h =the head of water, in feet, on the discharge siphon; hi =the initial head of water, in feet, on the siphon; /i2 = the final head of water in feet, on the siphon ; t =the time, in seconds, required to empty the tank, then dQ = Adh=qidt q 2 dt, dQ -Adh and dt=- - = , q qi-q* but qi=QAAV2Jjh, 1 C h * -Adh therefore t= but A =4/i 2 +46/i+& 2 , therefore t= QAaV2gh-q 2 From paper by E. G. Bradbury in Proceedings of the Ohio Eng. Society, 1910, p. 79. 450 FILTRATION AND IRRIGATION The integration of this expression is tedious. Its solution for siphons between 6 inches and 12 inches operating under heads commencing from 3 feet to 6 feet, with a time of emptying of 5 minutes and time of filling of 10 minutes is given in Fig. 173. In the example given the rate of inflow is 1.55 sec. feet and the head is 5 feet. Then from Fig. 173 the size of the siphon to be used is 12 inches. Where a siphon of the size required Rate of Inflow; Cubic Feet per Second 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 .1.7 if 2000 7000 8000 3000 4000 5000 6000 Capacity of Tank in Gallons. FIG. 173. Diagram for the Determination of the Capacities of Dosing Tanks for Trickling Filters. Time of emptying, 5 minutes. Time of filling, 10 minutes. Shape of tank is a right pyramid or a truncated right pyramid with all four sides making an angle of 45 degrees with the ver- tical. All horizontal cross-sections are squares. to empty the tank in the time fixed is not available, combinations of available sizes can sometimes be used. For example, if the given head is 6 feet, and the rate of inflow is 1.4 sec. feet, it is evident from Fig. 173 that a 6,300-gallon dosing tank and two 8-inch siphons will give the required cycle. The method used for the design of the setting of Taylor nozzles by the Pacific Flush Tank Co., is less rational but more simple and probably as satisfactory. In this method the steps are as follows: (1) Divide the maximum daily rate of sewage flow by 1,000 to get the maximum minute inflow. THE TRICKLING FILTER 451 (2) The number of nozzles required is determined by dividing the preceding figure by 6. Generally a Taylor nozzle with an orifice of f of an inch will discharge about 20 g.p.m. at the high head and about 8 g.p.m. at the low head, and as the nozzles must have a capacity which will take care of the inflow at the low head, the divisor 6 is used as a factor of safety instead of using 8 as the divisor. (3) The type of nozzle to be used is selected from experience or as a matter of judgment. Circular-spray nozzles are more generally used. (4) The spacings are determined from Fig. 170. (5) The dosing tank of the shape described is then designed. The capacity is such as to give a complete cycle once every 15 minutes. The method of this design is similar to that followed previously. (6) The dosing siphons are designed so that they will have a capacity at the minimum head of from 40 to 50 per cent in excess of the maximum minute inflow, and the draining depth of the siphon will be limited to a maximum of 5 to 5J feet. The siphons are all made adjustable with a variation of 6 inches or more on either side of the normal discharge line so that the spraying area and cycle can be varied to secure the best results. The underdrainage of a trickling filter should consist of some form of false bottom such as the types shown in Fig. 174. Where possible the underdrains should be open at both ends for the purpose of ventilation and flushing. It is desirable that the drains be so arranged that a light can be seen through them in order that clogging can be easily located. The drains should be placed on a slope of approximately 2 in 100 towards a main collector. The length of the drains is limited by their capacity to carry the average dose from the area drained by them. The main collecting conduits must be designed in accordance with the hydraulic principles given in Chapter IV. No valves, or other controlling apparatus, are placed on the underdrains or outlets from the filter. Covers have been provided in winter for some trickling filters in cold climates. The Taylor sprinkling nozzle has been found to work successfully in extremely cold weather, and it is generally accepted that the covering of filters is unnecessary, if the filter is not to be shut down for any length of time in cold weather. 452 FILTRATION AND IRRIGATION The operation of devices for automatically controlling the operation of a trickling filter is explained in Chapter XXI. 258. Intermittent Sand Filter. An intermittent sand filter is a specially prepared bed of sand, or other fine grained material, on the surface of which sewage is applied intermittently, and from which the sewage is removed by a system of underdrains. It differs from broad irrigation in the character of the material, the care and preparation of the bed, and the thoroughness of the under drainage. A distinctive feature of the intermittent sand Staffed Vitrified Half Tvne i," Steel Mesh Reinforcement-' Mortar Joint^ ^--Vif. Clay Floor Block Type B. TypeC Type D. Type C-E. FIG. 174. Types of False Bottoms for Trickling Filters. Eng. News, Vol. 74, p. 5. filter is the quality of the effluent delivered by it. In a properly designed and operated plant the effluent is clear, colorless, odor- less, and sparkling. It is completely nitrified, is stable and con- tains a high percentage of dissolved oxygen. It contains no settleable solids except at widely separated periods when a small quantity may appear in the effluent. The percentage removal of bacteria may be from 98 to 99 per cent. Some analyses of sand filter effluents are given in Table 89. The dissolved solids, the remaining bacteria, and the antecedents of the effluent are the only differences between it and potable water. An effluent from an intermittent sand filter is the most highly purified INTERMITTENT SAND FILTER 453 P ixaie 01 Filtration, r~\ n 02 oT >i HQ S|& ' i i oo QOrH ; Or-i ; o o ' O5 "* t^ ' CO t^ Tf ;I-H 8 o : .'CO ;d CO O O rH TjH (M CO t^ rH i O OrH uxygen Dissolved ; co - CO CO N CO I 1 ( uxygeii Consumed OHO Oi'cd cd >O o 001^ CO CO I> O5 ^^ i-H ^2 CO iOI> Tt< 00 (N OS (N rH oo oo os k 00 ^ 1 1 iOCO OicOO iM CO COrH TjH OS COO CO (N 2 < |o O 53 J g rHCO rt<. -^ t>. fe _> ll OG o S T 1 i i 1 Nitrites ooo OrH O O I-H o os i-H i-HO oo o :8 : iH OSrH COO rH CO i-HO OS ^ t>- rH CO IO O rH -H CO CO 1-1 iO T-H l> CO ^f rH iO i I 1C CO CO ^ rH COrH (N rH OON co CO rJH rH NrH [JALITY OF I ge Purificati Free Ammonia . CO O rH T ( ^ ^ (N co c^i (N ^O CO CO "t "* 00 (N (N CO O b- I> O OSI>-t O5(N Tt^CO & g J| : : : i pM c3 . . . . n " fl h * 6 S 1 : bD fl -4-3 ... O ^d s rainer. . 1 : : : : 3 ! I ! ! | : : : : 2 02 CJ c 1 o . . +2 3 * o ! CO o> o3 ^ d .g . . . . 3 & Ij i i 8 : 8 : : : & : : : : B s g . . . g s S : : : S : : : : 8 o ..- 2 2 2 < ' : : 5 g ^ .2 ^ ^ ^ ter influenl ter effluent ter effluenl ter influenl ter effluenl ter effluenl ter effluent ter influenl ter effluent ter influenl ter effluent ter influenl ter effluent ter effluent ter effluent Mill * l^cSE as Mfl %4 % % ^1^^^ sss ss s sss 454 FILTRATION AND IRRIGATION effluent delivered by any form of sewage treatment. The effluent can be disposed of without dilution, on account of its high stability. The treatment of sewage to so high a degree is seldom required, so that the use of intermittent niters is not common. Other drawbacks to their use are the relatively large area of land necessary and the difficulty of obtaining good filter sand in all localities. The action in an intermittent sand filter is more complete than in other forms of filters because a greater surface is exposed to the passage of sewage by the fine sand particles, and the sewage is in contact with the filtering material a longer time due to the lower rate of filtration and the slow velocity of flow through the filter. It is essential that the sewage be applied to the bed intermittently in order that air shall be entrained in the filter. The period between doses should not be so long that the filter becomes dry. In the operation of an intermittent sand filter one dose per day is considered an ordinary rate of application, although some plants operate with as many as four doses per day per filter, and others on one dose at long and irregular intervals. It is not always necessary to rest the filter for any length of time unless signs of overloading and clogging are shown. The intermittent dosing action may be obtained by the action of an automatic siphon as is described in Chapter XXI. The sewage is distributed on the beds through a number of openings in the sides of distribut- ing troughs resting on the surface of the filter. The sewage is withdrawn from the bottom of the filter through a system of underdrains, into which it enters after its passage through the bed. There are no control devices on the outlet, as the rate of filtration is controlled by the action of the dosing apparatus and the rate at which sewage is delivered to it. The action of the dosing apparatus should respond quickly to variations in sewage flow. As the doses are applied to a sand filter, a mat of organic matter or bacterial zooglea is formed on the surface of the bed. The mat is held together by hair, paper, and the tenacity of the materials. It may attain a thickness of J to \ an inch before it is necessary to remove it. So long as the filter is draining with sufficient rapidity this mat need not be removed, but if the bed shows signs of clogging, the only cleaning that may be necessary will be the rolling up of this dried mat. It INTERMITTENT SAND FILTER 455 is believed that the greater portion of the action in the filter occurs in the upper 5 to 8 inches of the bed, but occasionally the beds become so clogged that it is necessary to remove f of an inch to 2 inches of sand in addition to the surface mat, or to loosen up the surface by shallow plowing or harrowing. The necessity for such treatment may indicate that the filter is being overloaded as a result of which the rate of filtration should be decreased or the preliminary treatment should be improved. The plowing of clogging material into the bed should be avoided as under these conditions the final condition of the bed will be worse than its condition when trouble was first observed. In winter the surface of the bed should be plowed up into ridges and valleys. The freezing sewage forms a roof of ice which rests on the ridges and the subsequent applications of sewage find their way into the filter through the valleys under the ice. In a properly operated bed the filtering material will last indefinitely without change. If a filter is operated at too high a rate, however, although the quality of the effluent may be satisfactory, it will be necessary at some time to remove the sand and restore the filter. The rate of filtration depends on the character of the influent, the desired quality of the effluent, and the depth and character of the filtering material. Filters can be found operating at rates of 50,000 gallons per acre per day and others at eight times this rate. For sewage which has had some preliminary treatment, the rate should not exceed 100,000 gallons per acre per day, whereas the rate for raw sewage should be less than this. For rough estimates made without tests of the sewage in question, the rate should not be taken at more than 1,000 persons per acre. If the preliminary treatment of the sewage has been thorough and the material of the sand filter is coarser than ordinary the rate of filtration can be high. For less careful preliminary treatment and fine filtering material the rates must be reduced. The sewage must undergo sufficient preliminary treatment to remove large particles of solid matter which would otherwise clog the dosing apparatus and the filter. This treatment should include grit removal, screening, and some form of tank treatment. Some plants have operated successfully with a stale sewage and no preliminary treatment, as at Brockton, Mass. Septic tank effluent can be treated successfully on an intermittent sand 456 FILTRATION AND IRRIGATION filter, but not so satisfactorily as the effluent from a tank delivering a fresh sewage. The material of the filter should consist of clean, sharp, quartz or silica sand with an effective size x of 0.2 to 0.4 mm., preferably about 0.25 to 0.35 mm., and a uniformity coefficient 2 of 2 to 4. Within the limits mentioned no careful attention need be given to the size of the material. Natural sand found in place has been underdrained and used successfully for sewage treatment. The size of the sand is fixed by the rate of filtra- tion rather than the bacteriological action of the filter. A coarse sand will permit the sewage to pass through the bed too rapidly, and a fine sand will hold it too long or will become clogged. The same size of material should be used throughout the bed, except that a layer of gravel from 6 to 12 inches thick, graded from very small sizes to stones just passing a 2-inch ring should be placed at the bottom to facilitate the drainage of the bed. The thickness of the sand layer should not be less than 30 inches to insure complete treatment of the sewage. In shallower beds the sewage might trickle through without adequate treat- ment. Beds are ordinarily made from 30 to 36 inches deep, but when deeper layers of sand are found in place there is no set limit to the depth which may be used. The shape and overall dimensions of the bed should conform to the topography of the site and the rate of filtration adopted. A plan and cross-section of an intermittent sand filter showing the distribution and underdrainage systems are given in Fig. 166 and 175. The distribution system consists of a system of troughs on the surface of the filter, laid out in a branching form, as shown in the figure. The openings in the troughs should be so located that the maximum distance from any point on the bed to the nearest opening should not exceed 20 to 30 feet. If the filters are small enough, troughs need not be used, the sewage being distributed from one corner, or from mid-points on the sides. Where troughs are used they should be supported from 1 The effective size of sand is the diameter in millimeters of the largest grain in that 10 per cent, by weight, of the material which contains the smallest grains. 2 The uniformity coefficient is the ratio of the diameter of the largest particle of the smallest 60 per cent, by weight, to the effective size. INTERMITTENT SAND FILTER 457 the bottom of the filter in order to prevent uneven settling due to the washing of the sand. The openings in the troughs are made adjustable by swinging gates as shown in Fig. 176, or by other means so that after the filter is in operation the intensity of the dose on any portion of the filter can be changed. The troughs may be placed with their bottoms level with the surface of the sand and with sides of sufficient height to give the required gra- dient to the water surface, or they may be built up above the sur- Section on Line A-B. FIG. 175. Plan and Section of an Intermittent Sand Filter Showing Central Location of Control House. face of the filter and given the required slope so that the surface of the flowing water is parallel to the bottom of the trough. In either case a splash plate should be placed at each opening, so that not less than 2 feet of the surface of the sand is protected in all directions from the opening. A stone or concrete slab 2 to 4 inches thick makes a satisfactory splash plate. Either wood or concrete may be used for the construction of the troughs. The former is less durable, but also less expensive 458 FILTRATION AND IRRIGATION in first cost. The capacity of the troughs may be computed by Kutter's formula with the quantity to be carried equal to the maximum rate of discharge of the feeding siphon, with a reduc- tion in size below each branch or outlet proportional to the amount which will be discharged above this point. The operation of automatic devices for dosing the bed is explained in Chapter XXI. The dosing tank should have a capacity sufficient to cover the bed to a depth of about 1 to 3 inches at one dose, and the siphon should discharge at a rate of about one second-foot for each 5,000 square feet of filter area. A dose should disappear within 20 minutes to half an hour after it is applied to the filter. With the rate stated and four appli- FIG. 176. Distributing Trough with Adjustable Openings. cations per day to a depth of 1 inch at each dose, the rate per acre per day will be 109,000 gallons. The filtration of sewage through sand in a manner similar to the rapid sand filtration of water is being attempted at the Great Lakes Naval Training Station. No results of this treat- ment have been published and the practical success of the method has not been assured. 259. Cost of Filtration. Only comparative figures can be given in stating the costs of filtration, as most data available are based on pre-war conditions, and are therefore unreliable for present conditions. The variations from the figures given may be very large but in general the relative costs have not changed. The figures given in Table 90 are suggestive of the rela- tive costs of the different forms, of filtration. THE PROCESS 459 TABLE 90 RELATIVE COSTS OF DIFFERENT METHODS OF SEWAGE TREATMENT Costs in Dollars per Million Gallons per Day Operation Form of Treatment First Cost * and Total Maintenance Coarse screens 20 Fine screens 3.00 Plain sedimentation 7.00 3.00 10.00 Chemical precipitation 22 00 f Septic tank 7.00 1.00 8.00 Imhoff tank 10.00. 1.00 11.00 Contact bed 8 00 2 00 10 00 Trickling filter 4.00 2.00 6 00 Intermittent sand filter 15.00 10.00 25 . 00 Activated sludge 6 50 8 50 15 OOt * Interest at 6 per cent, the sale of sludge. f Worcester figures. t This method may show a profit from IRRIGATION 260. The Process. Broad irrigation is the discharge of sewage upon the surface of the ground, from which a part of the sewage evaporates and through which the remainder perco- lates, ultimately to escape in surface drainage channels. Sewage farming is broad irrigation practiced with the object of raising crops. Broad irrigation can be accomplished successfully with- out the growing of crops, but it is seldom attempted as some return and sometimes even a profit can be obtained from the crops raised. Broad irrigation and sewage farming differ from intermittent sand filtration in the intensity of the application of the sewage, the method of preparing the area on which the sewage is to be treated, and the care in operation. In broad irrigation and intermittent sand filtration the paramount con- sideration is successful disposal of the sewage. In sewage farming the paramount consideration is the growing of crops. The growing of crops may be combined with irrigation and filtration, however, but the crop should be sacrificed to the successful disposal of the sewage. 460 FILTRATION AND IRRIGATION The change which occurs in the characteristics of the sewage due to its filtration through the ground is the same as occurs in aerobic filtration. The effect on the crops is mainly that of an irrigant, as the manurial value of the sewage is small. 261. Status. The disposal of sewage by broad irrigation was practiced in England previous to the development of any of the more intensive biologic methods of treatment. It was con- sidered the only safe and sanitary method for the disposal of sewage, and as a result, areas irrigated by sewage were common throughout England. Crops were grown on these areas as a minor consideration, and sewage farming gained some of its popularity from the apparent success of these disposal areas. The success of sewage farms is due more to generous irrigation in dry years than to fertilization by sewage. The sewage farms of Paris and Berlin are frequently cited as examples of the successful and remunerative disposal of sewage by farming in connection with broad irrigation. Kinni- cutt, Winslow, and Pratt l state: The Berlin Sewage farms offer examples of broad irrigation under better conditions ... of 21,008 acres receiving sewage, 16,657 acres were farmed by the city, 3,956 acres were leased to farmers, and only 395 acres were unproductive. The contributing population at this time was 2,064,000 and the average amount of sewage treated was 77,000,000 gallons, giving a daily rate of treatment of about 3,700 gallons per acre of prepared land. The soil is sandy and of excellent quality. A quarter of the area operated by the authorities is devoted to pasturage, and about a third to the cultivation of cereals, of which winter rye and oats are the most important. Potatoes and beets are grown in considerable amounts and a wide variety of other crops in smaller proportions. . . . Even fish ponds are made to yield a part of the revenue, and the drains on some of the farms have been successfully stocked with breed trout. The cost of the Berlin farms to March 31, 1910, was $17,470,000, somewhat more than half being the purchase price of the land. The expenses for this year amounted to $1,300,385 for maintenance, and $741,818 for interest charges. The receipts were $1,240,773 and there was an estimated increase of $122,593 in value of live stock and other property. 1 Sewage Disposal, 1919, p. 223. PREPARATION AND OPERATION 461 The conditions at Berlin are quoted at length to indicate the success which can accompany broad irrigation, and as an example of what is being done abroad, where the rainfall is light and the soil is suitable. In the United States success in sewage farming has not been marked. This may be due partially to the relative weakness of American sewages, to the cost of labor, to lack of satisfactory irrigation areas, and to inattention to details. An attempt was made to grow crops on the sand filters at Brockton, Mass., but it was finally abandoned as the interests of the crops and the successful treatment of the sewage could not both be satisfied. At Pullman, Illinois, 1 in 1880, there was commenced probably the most extensive attempt at sewage farming in eastern United States. The farm was a failure from the start, because of the clay soil, and it was subsequently abandoned. Sewage farming, mainly as a subsidiary consideration to the filtration of sewage, is practiced in a few cities in the eastern portion of the United States to-day. Among the cities mentioned by Met calf and Eddy 2 are Danbury, Conn., and Fostoria, Ohio. In the western portion of the United States where water is scarce and the ground is porous, sewage has been used as an irri- gant with some success. Such use of sewage cannot be considered as a method of treatment since the prime consideration is the growing of crops. In this process all sewage not used as an irrigant is discharged without treatment into water courses. According to Met calf and Eddy there were 35 cities in Cali- fornia in 1914 that were operating sewage farms. Among these are Pasadena, Fresno, and Pomona. Other farms, notably the pioneer farm at Cheyenne, Wyo., have been abandoned because of the local nuisance created and the lack of financial success. 262. Preparation and Operation. A porous sandy soil on a good slope and with good underdrainage is most suitable for broad irrigation. Impervious clay or gumbo soils are unsuitable and should not be used. They become clogged at the surface, forming pools of putrefying sewage, or in hot weather form cracks which may permit untreated sewage to escape into the underdrains. The sewage may be distributed to the irrigated area in any 1 See Eng. News, Vol. 9, 1883, p. 203, and Vol. 29, 1893, p. 27. 2 American Sewerage Practice, Vol. III. 462 FILTRATION AND IRRIGATION one of five ways which are known as: flooding, surface irriga- tion, ridge and furrow irrigation, filtration, and sub-surface irrigation. In flooding, sewage is applied to a level area surrounded by low dikes. The depth of the dose may be from 1 inch to 2 feet. In surface irrigation the sewage is allowed to overflow from a ditch over the surface of the ground into which it sinks or over which it flows into another ditch placed lower down. This ditch conducts it to a point of disposal or to another area requiring irrigation. Ridge and furrow irrigation consists in plowing a field into ridges and furrows and filling the furrows with sewage while crops are grown on or between the ridges. In filtration the sewage is distributed in any desired fashion on the surface and is collected by a system of underdrains after it has filtered through the soil. In subsurface irrigation the sewage is applied to the land through a system of open joint pipes laid immediately below the surface, similarly to a system of under- drains. Combinations of and modifications to these methods are sometimes made. Underdrains may be used in connection with any of these forms of distribution. The preparation of the ground consists in: the construction of ditches or dikes to permit of any of the above described methods of application, grading of the surface to prevent pooling, the laying of underdrains, and the grubbing and clearing of the land. The main carriers may be excavated in open earth or earth lined with an impervious material. The distribution of the sewage from the main carriers to groups of laterals may be controlled by hand-operated stop planks. If the soil has a tendency to become waterlogged it may be relieved by install- ing underdrains at depths of 3 to 6 feet, and 40 to 100 feet apart. The tile underdrains may discharge into open ditches excavated for the purpose which serve also to drain the land. Drains should be used where the ground water is within 4 feet of the surface, and the open ditches should be cut below the drains to keep the ground water out of them. Four or 6-inch open-joint farm tile may be used for underdrains. The porosity of the soil will be increased by cultivation. Where particular care is taken in the cultivation of the soil so that sewage can be applied at a high rate, broad irrigation merges into the more intensive intermittent filtration through sand. Before being turned on to the land, sewage should be screened SANITARY ASPECTS 463 and heavy-settling particles should be removed. The rate of application may be increased as the intensity of the preliminary treatment is increased. The rate at which sewage may be applied is dependent also on the character of the soil, and may vary between 4,000 and 30,000 gallons per acre per day, although higher rates have been used with the effluent from treatment plants and on favorable soil. The sewage should be applied intermittently in doses, the time between doses varying between one day and two or three weeks or more, dependent on the weather and the condition of the soil. The methods of dosing vary as widely as the rates. The dose may be applied con- tinuously for one or two weeks with correspondingly long rests, or it may be applied with frequent intermittency alternated with short rests, interspersed with long rest periods at longer intervals of time. When applying the sewage to the land the rate of application of the dose is about 10,000 to 150,000 gallons per acre per day. The area under irrigation at any one time may be as much as 10 to 15 acres. The rate of the application of the sewage is also dependent on the weather and may vary widely between seasons. It is obvious that a rain-soaked pasture cannot receive a large dose of sewage without danger of undue flooding. One of the principal difficulties with the treatment or disposal of sewage by broad irrigation is that the greatest load of sewage must be cared for in wet seasons when the ground is least able to absorb the additional moisture. 263. Sanitary Aspects. A well-operated sewage farm should cause no offense to the eye or nose, and is not a danger to the public health. In Berlin, a portion of the sewage farms are laid out as city parks. The liquid in the drainage ditches or underdrains may be clear, odorless, and colorless, high in nitrates and non-putrescible. Where the farm has been improperly managed or overdosed the condition may be serious from both esthetic and health considerations. Sewage may be spread out to pollute the atmosphere and to supply breeding places for flying insects which will spread the filth for long distances sur- rounding the farm. The character of the crop is also a sani- tary consideration. 264. The Crop. From a sanitary viewpoint no crops which come in contact with the sewage should be cultivated on a sewage farm. Such products as lettuce, strawberries, asparagus, 464 FILTRATION AND IRRIGATION potatoes, radishes, etc., should not be grown. Grains, fruits, and nuts are grown successfully and as they do not come in con- tact with the sewage there is no sanitary objection to their cultivation in this manner. Italian rye grass and other forms of hay are grown with the best success as they will stand a large amount of water without injury. The raising of stock is also advisable for sewage farms where hay and grain are culti- vated. The stock should be fed with the fodder raised on the irrigated lands and should not be allowed to graze on the crops during the time that they are being irrigated. This is due as much to the danger of injury to the distributing ditches and the formation of bogs by the trampling of the cattle, as to the danger to the health of the cattle. CHAPTER XVIII ACTIVATED SLUDGE 265. The Process. In the treatment of sewage by the activated sludge process the sewage enters an aeration tank after it has been screened and grit has been removed. As it enters the aeration tank it is mixed with about 30 per cent of its volume of activated sludge. The sewage passes through the aeration tank in about two to four hours during which time air is blown through it in finely divided bubbles. The effluent from the aeration tank passes to a sedimentation tank where it remains for one-half an hour to an hour to allow the sedimen- tation of the activated sludge. The supernatant liquid from the sedimentation tank is passed to the point of final disposal. A portion of the sludge removed from the tank is returned to the influent of the aeration tank. The remainder may be sent to any or all of the following: the sludge drying process, the reaera- tion tanks, or to some point for final disposal. Sections of the activated sludge plant at Houston, Texas, are shown in Fig. 177. The biological changes in the process occur in the aeration tank. These changes are dependent on the aerobic organisms which are intensively cultivated in the activated sludge. When placed in intimate contact with fresh sewage, brought about by the agitation caused by the rising air, and in the presence of an abundance of oxygen, the organic matter is partially oxidized. The putrefactive stage of the organic cycle is avoided. Col- loids and bacteria are partially removed probably by the agita- tion effected in the presence of activated sludge but the exact action which takes place is not well understood. 266. Composition. Activated sludge is the material obtained by agitating ordinary sewage with air until the sludge has assumed a flocculent appearance, will settle quickly, and contain aerobic and facultative bacteria in such numbers that similar characteristics can be readily imparted to ordinary sewage 465 466 ACTIVATED SLUDGE sludge when agitated with air in the presence of activated sludge. Copeland described activated sludge as follows: 1 The sludge embodied in sewage and consisting of suspended organic solids', including those of a colloidal nature, when agitated with air for a sufficient period assumes a flocculent appearance very similar to small pieces of sponge Aerobic and facultative bacteria gather in these flocculi in immense numbers from 12 to 14 /Sludge Return Channel^ 8"Sluice Part Plan of Outside Unit Aeration and Settling Tank. ' spi : niffirl MlM dawr/flS// t23a CHAMBER f te^/-^'-1 SLUDGE TANK H^ ^vo U^.vAU.^vJ ^_^^ v ^ v ^ 58- 6 "for North <5ide Plank >i| . S9-0" South -*) Half Section through Aeration Tanks Half Sec-tion through Settling Tanks. FIG. 177. Activated Sludge Plant at Houston, Texas. Eng. News, Vol. 77, p. 236. million per c.c. some having been strained from the sewage and others developed by natural growth. Among the latter are species that have the power to decompose organic matter, especially of an albuminoid or nitrog- enous nature, setting the nitrogen free; and others absorbing the nitrogen convert it into nitrites and nitrates. These biological processes require time, air, and favorable environment such as suitable temperature, 1 Reference 11, at end of this chapter. COMPOSITION 467 food supply and sufficient agitation to distribute them throughout all parts of the sewage. Ardern states that the sludge differs entirely from the usual tank sludge. It is inoffensive and flocculent in character. The percentage of moisture is from 95 to 99 per cent. American experience has generally been that the sludge does not readily separate from its moisture by treatment on fine-grain filters, but the results in England and at Milwaukee, Wisconsin, are in conflict with this general experience. Upon standing 24 hours or more partially dried activated sludge may start to decompose accompanied by the production of offensive odors. Duckworth states : The activated sludge at Salford contained three times as much nitrogen, twice as much phosphoric acid and one-half as much fa .y matter as ordinary sludge. TABLE 91 COMPOSITION OF SEWAGE, IMHOFF SLUDGE, AND ACTIVATED SLUDGE AND EFFLUENT AT MILWAUKEE (W. R. Copeland, Eng. News, Vol. 76, p. 665) Parts per Million & Nitrogen as Period of Source of 03 g Nitrogen Reported as Ammonia on a Test Sample "8 .5 e 1-3 c o 1 Basis of Sludge Dried to 10 Per d g fa +3 S Cent Moisture. 1 >J II & Three samples of Sludge 02 < 6 z 2 Aug., 1915. Sewage 253 14.6 7.88 29 0.15 0.13 Imhoff effluent. . 105 16.2 6.10 27 0.19 0.13 2.87 3.82 Activated sludge effluent 14 3.8 3.19 6 0.29 6.00 5.71 4.97 7.04 Sept., 1915. Sewage 300 13.5 8.81 29 0.25 0.14 Imhoff effluent. . 116 15.4 7.10 27 0.12 0.09 3.88 Activated sludge effluent 8 5.7 2.22 9 0.24 5.01 8.69 9.00 These results have been roughly checked by American experi- menters as shown in Table 9 1. 1 In the recovery of nitrogen from sewage the activated sludge process is the most promising for satisfactory results. In all other processes of sewage treat- 1 Reference 15. 468 ACTIVATED SLUDGE ment the sludge is digested to some extent and nitrogen lost in the gases or in the soluble matter which passes off with the effluent. In the activated sludge process a negligible amount of gasification and liquefaction take place and only a small amount of nitrogen passes off with the effluent as compared with the loss from the Imhoff process as shown in Table 91. The percentage of nitrogen in dried activated sludge is shown in Table 92. TABLE 92 NITROGEN CONTENT OF DRY ACTIVATED SLUDGE AND SLUDGE FROM OTHER PROCESSES (G. W. Fuller, Eng. News, Vol. 76, p. 667) Source Per Cent Nitrogen Milwaukee (Copeland) Manchester, England (Ardern) 4.40 4 60 Salford, England (Melling) 3.75 Urbana, Illinois (Bartow) Armour and Co. (Noble) 3.5to 6.4 4.6 Approximate range of all other processes . l.OtoS.O These figures are expressed in terms of nitrogen and not of ammonia. Nitrogen is only 82 per cent of the ammonia content, Nitrifying bacteria and other species which have the power of destroying organic matter have been isolated from the sludge. An analysis of the dried sludge at Urbana l showed the following results after the weight had been reduced 95.5 per cent by drying: 6.3 per cent nitrogen, 4.00 per cent fat, 1.44 per cent phosphorus, and 75 per cent volatile matter or loss on ignition. Analyses of other domestic sewages have not shown such high contents of these desirable constituents. The dewatering of activated sludge is a problem which offers serious obstacles to the successful operation of the process. It is its greatest disadvantage. Five to ten times the volume of sludge may be produced by the activated sludge process as by an Imhoff tank, and the activated sludge contains a greater percentage of water. According to Copeland: 1 Reference 2. ADVANTAGES AND DISADVANTAGES 469 The best information now available points to a combination of settling and decantation as a preliminary dewatering process. By this means the water will be cut down from about 99 per cent to 96 per cent. On passing the concentrated residue through a pressure filter the moisture can be cut down to 75 per cent. The press cake can be dewatered in a heat drier to 10 per cent moisture or less, 1 The quantity of sludge produced at Milwaukee 2 is about 15 cubic yards per million gallons of sewage, the sludge having about 98 per cent moisture. On the basis of 10 per cent mois- ture it produces \ ton of dry sludge per million gallons of sewage treated. At Cleveland, 3 20 cubic yards per million gallons at 97.5 per cent moisture are produced. Methods of drying sludge are discussed in Chapter XX. Chemical analyses and biological tests indicate that the fertilizing value of the sludge is appreciable. Professor C. B. Lipman states, as the result of a series of tests in which a sludge and a soil were incubated for one month, as follows: 4 The amounts of nitrates produced in one month's incubation from the soil's own nitrogen and from the nitrogen from the sludge mixed with the soil in the ratio of one part of sludge to 100 of soil is, in milligrams of nitrate, as follows: Anaheim soil without sludge 6.0, with sludge 10.0; Davis soil without sludge 4.2, with sludge 14.0; Oakley soil without sludge 2.2, with sludge 4.0. The effect of the sludge on plant growth is shown in Table 93. 5 The results represent the growth obtained after fifteen weeks from the planting of 30 wheat seeds in each pot. 267. Advantages and Disadvantages. Some of the advantages of the process are : a clear, sparkling, and non-putrescible effluent is obtained; the degree of nitrification is controllable within certain limits; the character of the effluent can be varied to accord with the quantity and character of the diluting water 1 For mechanical methods of drying sludge, see Reference 22, p. 1127, and No. 33, p. 843. 2 Reference 10. 3 Reference 13. 4 University of California, Bulletin 251, 1915. 6 Reference 25. 470 ACTIVATED SLUDGE available; more than 90 per cent of the bacteria can be removed; the cost of installation is relatively low; and the sludge has some commercial value. TABLE 93 FERTILIZING VALUE OF ACTIVATED SLUDGE (E. Bartow, Journal Am. Water Works Ass'n, Vol. 3, p. 327) Cultivating Medium Grams Contained in Experimental Pot 1 2 3 4 White sand 19,820 60 6 3 19,820 60 6 3 8.61 19,820 60 6 3 20 19,820 60 6 3 20 Dolomite Bone meal . . Potassium sulphate Activated sludge Activated sludge extracted with Ligroin Dried blood Number of heads of wheat. Number of seeds Weight of seeds, grams .... Bushels per acre, calculated. Average length of stalk, inches 14 85 2.38 6.20 19.40 2.25 0.18 15 189 5.29 13.6 23.0 8.25 0.68 22 491 13.748 35.9 35.4 26.75 2.23 23 518 14.504 38.7 37.1 26.21 2.18 Weight of straw, grams. . . Tons per acre, calculated . . . Among the disadvantages of the process can be included, uncertainty due to the lack of information concerning the results to be expected under all conditions, high cost of operation under certain conditions, the necessity for constant and skilled attendance, and the difficulty of dewatering the sludge. 268. Historical. The most notable work in the aeration Of sewage within recent years was that performed by Black and Phelps for the Metropolitan Sewerage Commission of New York, in 1910, 1 and by Clark and Gage at the Lawrence, Massachusetts, Sewage Experiment Station in 1912 and 1913. 2 The results of 1 See Report by Black & Phelps of Metropolitan Sewerage Commission, 1911, reprinted as Vol. VII of Contributions from the Sanitary Research Laboratory of the Massachusetts Institute of Technology. 2 See Reports, Mass. State Board of Health. AERATION TANK 471 these investigations showed that the treatment of sewage by forced aeration might give a satisfactory effluent, but that the time and expense in connection thereto rendered the method impractical. It remained for Messrs. Ardern and Lockett of Manchester, England, to introduce the process of the aeration of sewage in the presence of activated sludge, as a result of their connection with Dr. Fowler, who attributes his inspiration to his visit to the Lawrence Experiment Station and observing the work of Clark and Gage. Ardern and Lockett commenced their experi- ments in 1913. Their results were published in the Journal of the Society of Chemical Industry, May 30, 1914, Vol. 33, p. 523. Shortly thereafter experiments were started at the University of Illinois by Dr. Edw. Bartow and Mr. F. W. Mohlmann of the Illinois State Water Survey. At about the same time an experi- mental plant was started at Milwaukee, by T. C. Hatton, Chief Engineer of the Milwaukee Sewerage Commission. The United States Public Health Service became actively interested in December, 1914, and on February 20, 1915, announced its intention to co-operate with the Baltimore Sewerage Commission in the conduct of experiments. In May, 1915, patent number 1,139,024 was granted to Leslie C. Frank, Sanitary Engineer of the U. S. Public Health Service, covering certain features of the process. Mr. Frank generously donated this patent to the public for the use of municipalities. The first full sized plant for the treatment of sewage by this method was erected in Milwaukee in December, 1915. This plant had a capacity of 1,600,000 gallons per day. It was used for experimental purposes and is not now in use. The Champaign, Illinois, septic tank, among the first of its kind in the country, was converted into an activated sludge tank on April 13, 1916. The changes, developments, and the results obtained from these and other plants have been reported in the technical press from time to time. 269. Aeration Tank. The sewage on leaving the screen and grit chamber enters the aeration tank, which is usually operated on the continuous-flow principle, although in the early days of experimentation the fill-and-draw method was practiced. This tank should be rectangular with a depth of about 15 feet and a width of channel not to exceed 6 to 8 feet. Such proportions 472 ACTIVATED SLUDGE allow better air and current distribution than larger tanks. The bottom should be level to insure an even distribution of air. The velocity of flow of sewage through the tank is usually in the neighborhood of 5 feet per minute, dependent on the length of the tank and the period of retention. The period of retention is in turn dependent on the desired quality of the effluent. The process is flexible and the quality of the effluent can be changed by changing the period of retention or by changing the rate of application of the air, or both. The period of retention in the aeration tank is usually about 4 hours. The bottom of the aeration tank is usually made of concrete arranged in ridges and valleys, or small shallow hoppers, at the bottom of which the air-diffusing devices are located, as shown in Fig. 177. The inlet and outlet devices are similar to those in a plain sedimentation tank. 270. Sedimentation Tank. It is evident that as no sedi- mentation is permitted in the aeration tank, the settleable parti- cles will be discharged in the effluent unless some provision is made for their detention. The effluent from the aeration tank is therefore run through a plain sedimentation tank, usually with a hopper bottom, which has been arranged to permit fre- quent and easy cleaning. An air lift or a centrifugal sludge pump is satisfactory for this purpose. Another type of sedi- mentation tank which has been used has a smooth bottom with a slight slope towards the center. A revolving scraper collects the sludge continuously, scraping it towards the center of the tank. Although this arrangement gives better results than the hopper-bottom tank, its expense has usually prevented its instal- lation. 1 The period of sedimentation in different plants varies from 30 minutes to one hour, although the longer periods usually give the better results. Approximately 65 per cent of the sludge will settle in the first 10 minutes, 80 per cent in the first 30 minutes, and about 5 per cent more in the next half hour. The effluent from the sedimentation tank is ready for final disposal or if desired, for further treatment by some other method. The sludge, or a portion of it, is pumped back into the influent of the aeration tank, provided the sludge is in a satis- factory state of nitrification. Otherwise it should be pumped 1 Reference 47. THE REAERATION TANK 473 to the reaeration tanks. The remainder of the sludge which is not to be used in the process is ready for drying and final disposal. 271. Reaeration Tank. The purpose of the reaeration or sludge aeration tank is to reactivate the sludge which has gone through the aeration tank. During the process of the aeration of the sewage in the aeration tank the activated sludge may lose some of its qualities because of the deficiency of oxygen to maintain aerobic conditions. By blowing air through the sludge in the reaeration tank these properties are returned and the sludge made available to be pumped back into the aeration tank. The reactivation of the sludge obviates the necessity for supplying sufficient air to the entire mass of the sewage to maintain aerobic conditions, and results in an economy in the use of air. The use of mechanical agitators has also been attempted both in the reaeration and the aeration tanks with the expectation of saving in the use of air, but with indifferent success. It is difficult to say, without experimentation, what the size of the reaeration tank should be, as the necessary amount or reactivation is uncertain. In the experimental plant at Mil- waukee, there were eight units of aeration tanks, one sedimenta- tion tank, and two reaeration tanks, all of the same capacity and general design. This represents a ration of about one reaeration tank to four aeration tanks. 272. Air Distribution. Air is applied to the sewage at the bottom of the aeration tank at a pressure in the neighborhood of^.S to 6.0 pounds per square inch, dependent on the depth of the sewage, the loss of head through the distributing pipes, and the rate of application. In different experimental plants the pressure has varied from 3 to 30 pounds per square inch. Such pressures are on the line which divides the use of direct blowers for low pressures from turbo and reciprocating pressure machines for pressures above 10 pounds per square inch. Posi- tive-pressure blowers or direct blowers operate on the principle of a centrifugal pump and because of the lighter specific gravity of air they rotate at a very high speed. The Nash Hytor Turbo Blower consists of a rotor with a large number of long teeth slightly bent in the direction of rotation. The rotor, which has a circular circumference, revolves in an elliptical casing. At the commencement of operation the rotor and casing are partially 474 ACTIVATED SLUDGE filled with water. The revolution of the rotor throws the water to the outside of the elliptical casing thus forming a partial vacuum between any two teeth as the water is thrown from near the center of the short diameter of the casing to the extremity of the long diameter of the casing. Air is allowed to enter through the inlet port to relieve the vacuum. As the teeth pass from the long diameter to the short diameter of the ellipse, the water again approaches the center of the rotor compressing the air trapped between the teeth and forcing ic out under pressure into tne ex- haust pipe. Among the ad- vantages of this compressor are the washing of the air, cooling, and ease in opera- tion. Reciprocating air com- pressors operate similarly to direct-acting steam pumps or crank - and - fly - wheel pumps but at much higher speeds, and they require more floor space than either of the other types. Fig. 178 shows the field of FIG. Volume Of Free Air in Thousands Cu. Ft per Minu+e 178. Economic Range of Air Com- pressors. From Eng. News, Vol. 74, p. 906. of various compression serviceability types of air machinery. For pressures up to about 10 pounds per square inch the posi- tive blower seems most desirable. It has a low first cost and a relatively high efficiency of about 75 to 80 per cent of the power input. No oil or dirt is added to the air to clog the distributing plates, as in the reciprocating machine. A disadvantage is the difficulty of varying the pressure or quantity of the output of the machine. As the required pressure and volume of air increases the turbo blower becomes more and more desirable within the limits of pressure which are ordinarily used in this process. For small installations the best form of power is probably the electric drive, but when the capacity becomes such as to make turbo blowers advisable they should be driven by directly connected steam turbines. AIR DISTRIBUTION 475 ( The quantity of air required varies between 0.5 to 6.0 cubic feet per gallon of sewage, with from 3 to 6 hours of aeration. The quantity of air depends on the degree of treatment required, the strength of the sewage, the depth of the tank, and the period of aeration. The deeper the tank the less the amount of air needed because of the greater travel of the bubble in passing through the sewage, but the higher the pressure at which the air must be delivered. Shallow tanks usually require a longer period of retention. The depth of the tank then has very little to do with economy in the use of air. Hatton states: 1 The purification of sewage obtained varies decidedly with the volume of air applied. Small volumes applied for 5 or 6 hours do as well as larger volumes applied for 3 or 4 hours, but the time of aeration required to obtain a like effluent does not vary directly with the volume of air applied per unit of time. For instance air applied at a rate of 2 cubic feet per minute purifies the sewage in less time than one cubic foot of air per minute, but will not accomplish an equal degree of purification in half the time, It has been found that although a low temperature has a dele- terious effect on the process, by the use of an additional quantity of air good results can be maintained. The effect of changing the quantity of air and the period of aeration are shown in Table 94 taken from Hatton. The velocity of the air in the pipes should be about 1,000 feet per minute. There should be relatively few sharp turns in the line, and the distributing mains should be arranged with- out dead ends. It is desirable to use as little piping as possible and at the same time to make the travel of the sewage long in order to maintain a non-settling velocity and intimate contact with the air. The piping should be accessible and well provided with valves. It should be non-corrodible, particularly on the inside, as flakes of rust will quickly clog the air diffusers. It should drain to one point in order that it can be emptied when flooded, as occasionally happens. It is desirable to diffuse the air in small bubbles as by this means the greatest efficiency seems to be obtained from the amount of air added, A diameter y^ to J of an inch is approxi- 1 Reference 10. 476 ACTIVATED SLUDGE s g PPLICATION OF AIR ON THE RE Y THE ACTIVATED SLUDGE PR (Milwaukee Results) Parts per Million l 11 ^ "84 8 -a II o o HI ;^gi 00 OSI> O O i-l TH iO CO O O O5 00 CO (N b- IO rH t~ 1O i 1 O5 T-H -H IO l> Tf O5 i 1 l> CO CO I>(M t^ i-l HOOOOO ' 00 AIR DISTRIBUTION 477 mately the maximum limit for the size of an effective bubble. Monel metal cloth, porous wood blocks, open jets, paddles, and other forms of diffusers have been tried, but none have given the satisfaction of the filtros plate. The relative value of dif- ferent types of diffusers is shown in Table 95 taken from Hatton. 1 The Filtros plates are a proprietary article manufactured by the General Filtration Company of Rochester, N. Y. They are made of a quartz sand firmly cemented together and can be TABLE 95 COMPARATIVE RESULTS FROM THE AERATION OP SEWAGE IN THE PRESENCE OF ACTIVATED SLUDGE WITH THE USE OF DIFFERENT DISTRIBUTING MEDIA (T. C. Hatton, Eng. Record, Vol. 73, p. 255) Pounds Air, Per Nitrates, Stability Diffusers Months in 1915 per Square Cubic Feet per Cent Bacteria Parts per Effluent in Inch Gallon Removed Million Hours Filtros plate June 1 to Aug. 15 4.3 2.06 91 3.4 78 Air jet June 1 to Aug. 15 3.5 1.94 91 2.2 52 Filtros plate Nov. 18 to Dec. 7 4.6 1.71 90 0.3 113 Monel metal Nov. 18 to Dec. 7 3.0 1.71 80 0.2 63 obtained with practically any degree of porosity, size of pore opening or dimension of plate, but they are made in a standard size 12 inches square by 1^ inches thick. The frictional loss through the plate is not very great for the amount of air ordi- narily used. The plates are classified in accordance with the volume of air which will pass through them, when dry, per minute when under a pressure of 2 inches of water. These classes run from J to 12 cubic feet of air per minute. The type usually specified passes about 2 cubic feet of air per minute. The loss of head through these plates as tested at Milwaukee showed an initial loss of J of a pound and an additional loss of about \ of a pound for every cubic foot of air per minute per square foot of surface. It is necessary to screen and wash the air before blowing it through the filtros plate as ordinary air is so filled with dirt as to clog the pores of the diffuser quite rapidly. 1 Reference 10. 478 ACTIVATED SLUDGE The area of filtros plates required in the bottom of the tank is usually expressed in terms of the free surface of the tank or as a ratio thereto. In the Urbana tests the best ratio was found to be less than 1 : 3 and more than 1:9. In Milwaukee 1 the ratio adopted is in the neighborhood of 1 : 4 or 1 : 5. At Fort Worth the ratio will be about 1 : 7 and at Chicago it will be 1:8. The exact ratio should be determined by experiment and will depend on the construction of the tank and the char- acter of the raw sewage and the desired effluent. It is essential that the filtros plates be placed level and at the same elevation as otherwise the distribution of air will be uneven. 273. Obtaining Activated Sludge. After a plant is once started activated sludge is generated during the process of treat- ment and with careful management a stock of activated sludge can be kept on hand. When a plant is new, or if shut down for such a length of time that the sludge loses its activation, it is necessary to activate some new sludge. This is done by blowing air continuously through sewage either on the fill and draw method with periodic decantations of the supernatant liquid, or by the continuous-flow process, but more preferably by the latter. Where activated sludge is to be obtained from fresh sewage alone the time required is in the neighborhood of 10 to 14 days, and purification begins at the start. An estimate of the quantity which will be obtained can not be made with accuracy. After the initial quantity of sludge has been obtained activated sludge can be maintained during the process of aeration of the raw sewage, or by means of the reaeration tanks previously described. The volume of activated sludge present in the aeration tank should be about 25 per cent of the volume of the tank. The volume of the sludge is measured in a somewhat arbitrary manner as the amount by volume which will settle in 30 minutes in an ordinary test tube. It is found that this is almost 90 per cent of the solids settling in 4 to 6 hours. 274. Cost. The available information on the cost of the activated sludge process is meager and unreliable. The factors entering into the cost are : the price of fuel, the size of the plant, the period of sedimentation, the amount of air per gallon of sewage, the air pressure, and the percentage of sludge to be aerated in the 1 Reference 10. COST 479 mixture. In Milwaukee 1 the cost of construction is estimated at $44,000 per million gallons, and $4.75 per million gallons for operation. At Houston, Texas, the cost is estimated at $24,000 per million gallons, exclusive of the sludge-drying plant, which may cost $40,000 per million gallons. At Milwaukee, the cost of pressing the sludge is $4.82 per dry ton and of drying is $3.93 per dry ton. The sludge may be sold at the normal rate of $2.50 per unit of nitrogen. Based on the normal value the evident profit will be $3.75 per ton. The net cost of disposing of Mil- waukee sewage is estimated at $9.64 per million gallons of which $4.89 is chargeable to overhead and $4.75 to repairs, operation and renewal. In a comparison of the costs of activated sludge and Imhoff tanks with sprinkling filters, 2 the information given by Eddy has been summarized in Table 96. In comparing the TABLE 96 COMPARATIVE COSTS OF ACTIVATED SLUDGE, AND OP IMHOFF TANKS FOLLOWED BY SPRINKLING FILTERS (H. P. Eddy, Eng. Record, Vol. 74, p. 557) Total Annual Cost at Process First Cost per Million Operation per Million 4 Per Cent with Sinking Fund at 2.5 Per Cent per Gallons, Gallons, Dollars Dollars Million Gallons, Dollars Capita, Dollars Activated sludge 57 100 20 00 29 85 1 09 Imhoff tank and sprinkling filter. 78,500 8.50 21.84 0.80 relative areas required for different methods of sewage treatment, activated sludge should be allowed about 15 million gallons per acre per day on the basis of aeration tanks 15 feet deep. This figure represents approximately the gross area of the plants at Milwaukee and at Cleveland. 1 Hatton, reference 33. 2 Reference 18. 480 ACTIVATED SLUDGE REFERENCES AND BIBLIOGRAPHY ON ACTIVATED SLUDGE The following abbreviations will be used: A.S. for Activated Sludge, E.G. for Engineering and Contracting, E.N. for Engineering News, E.R. for Engineering Record, E.N.R. for Engineering News-Record, p. for page, and V, for volume. No. 1. Cooperation Sought in Conducting A.S. Experiments at Baltimore, by Franks and Hendrick. E.R. V. 71, 1915, pp. 521, 724, and 784. V. 72, 1915, pp. 23, and 640. 2. Sewage Treatment Experiments with Aeration and A.S., by Bartow and Mohlman. E.N. V. 73, 1915, p. 647, and E.R. V. 71, 1915, p. 421. 3. A.S. Experiments at Milwaukee, Wisconsin, by Hatton. E.N. V. 74, 1915, p. 134. 4. A.S. in America, An Editorial Survey, by Baker. E.N. V. 74, 1915, p. 164. 5. Choosing Air Compressors for A.S., by Nordell, E.N. V. 74, 1915, p. 904. 6. A Year of A.S. at Milwaukee, by Fuller. E.N. V. 74, 1915, p. 1146. 7. A.S. Experiments at Urbana. E.N. V. 74, 1915, p. 1097. 8. Experiments on the A.S. Process, by Bartow and Mohlman. E.G. V. 44, 1915, p. 433. 9. Milwaukee's A.S. Plant, the Pioneer Large Scale Installation, by Hat- ton. E.R. V. 72, 1915, p. 481 and E.G. V. 44, 1915, p. 322. 10. A.S. Experiments at Milwaukee, by Hatton. Journal American Water- works Association and Proceedings Illinois Society of Engineers, 1916. Also E.R. V. 73, 1916, p. 255. E.G. V. 45, 1916, p. 104, and E.N. V. 75, 1916, pp. 262 and 306. 11. A.S. Defined. E.N. V. 75, 1916, p. 503, and E.N.R. V. 80, 1918, p. 205. 12. Status of A.S. Sewage Treatment, by Hammond. E.N. V. 75, 1916, p. 798. 13. Trial A.S. Unit at Cleveland, by Pratt. E.N. V. 75, 1916, p. 671. 14. Air Diffuser Experience with A.S. E.N. V. 76, 1916, p. 106. 15. Nitrogen from Sewage Sludge, Plain and Activated, by Copeland, Journal American Chemical Society, Sept. 28, 1916. E.N. V. 76, 1916, p. 665. E.R. V. 74, 1916, p. 444. 16. Tests Show A.S. Process Adapted to Treatment of Stock Yards Wastes. E.R. V. 74, 1916, p. 137. 17. Aeration Suggestions for Disposal of Sludge, by Hammond. Journal American Chemical Society, Sept. 25, 1916. E.R. V. 74, 1916, p. 448. 18. Cost Comparison of Sewage Treatment. Imhoff Tank and Sprinkling Filters vs. A.S., by Eddy. E.R. V. 74, 1916, p. 557. 19. Large A.S. Plant at Milwaukee. E.N. V. 76, 1916, p. 686. 20. A.S. Novelties at Hermosa Beach, Cal. E.N. V. 76, 1916, p. 890. 21. A.S. Experiments at University of Illinois, by Bartow, Mohlman, and Schnellbach. E.N. V. 76, 1916, p. 972. REFERENCES AND BIBLIOGRAPHY 481 No. 22. A.S. Results at Cleveland Reviewed, by Pratt and Gascoigne. E.N. V. 76, 1916, pp. 1061 and 1124. 23. Sewage Treatment by Aeration and Activation, by Hammond. Pro- ceedings American Society Municipal Improvements, 1916. 24. A.S., by Bartow and Mohlman, Proceedings Illinois Society of Engineers, 1916. 25. The Latest Method of Sewage Treatment, by Bartow. Journal Ameri- can Waterworks Association, V. 3, March, 1916, p. 327. 26. Winter Experiences with A.S., by Copeland. Journal American Society of Chemical Engineers, April 21, 1916. E.G. V. 45, 1916, p. 386. 27. A.S. Process Firmly Established, by Hatton. E.R. V. 75, 1917, p. 16. 28. Operate Continuous Flow A.S. Plant, by Bartow, Mohlman, and Schnellbach. E.R. V. 75, 1917, p. 380. 29. Chicago Stock Yards Sewage and A.S., by Lederer. Journal American Society of Chemical Engineers, April 21, 1916. E.G. V. 45, 1916, p. 388. 30. The Patent Situation Concerning A.S. E.G. V. 45, 1916, p. 208. 31. " Sewage Disposal " by Kinnicutt, Winslow, and Pratt, published by John Wiley & Sons. 2d Edition, Chapter 12. 32. A.S. Tests Made by California Cities. E.N.R. V. 79, 1917, p. 1009. 33. Conclusions on the A.S. Process at Milwaukee. Journal American Public Health Association, 1917. E.N.R. V. 79, 1917, p. 840. 34. Dewatering A.S. at Urbana, by Bartow. Journal American Institute of Chemical Engineers, 1917. E.N.R. V. 79, 1917, p. 269. 35. Milwaukee Air Diffusion Studies in A.S. E.N.R. V. 78, 1917, p. 628. 36. A.S. Bibliography (up to May 1, 1917) by J. E. Porter. 37. Air Diffusion in A.S. E.N.R. V. 78, 1917, p. 255. 38. A.S. Plant at Houston, Texas. E.N. V. 77, 1917, p. 236, E.N.R. 83, 1919, p. 1003, and V. 84, 1920, p. 75. 39. A.S. Power Costs, by Requardt. E.N. V. 77, 1917, p. 18. 40. A.S. at San Marcos, Texas, by Elrod. E.N. V. 77, 1917, p. 249. 41. Filtros Plates Made the Best Showing in Air Diffuser Tests. E.N.R. V. 79, 1917, 269. 42. Results of Experiments on A.S., by Ardern and Lockett. Journal Society for Chemical Research, V. 33, May 30, 1914, p. 523. 43. Final Plans at Milwaukee. E.N.R. V. 84, 1920, p. 990. 44. A.S. Bibliography, published by General Filtration Co., Rochester, N. Y., 1921. 45. A.S. at Manchester, Eng. by Ardern. Journal Society Chemical Indus- try, 1921. E.G. V. 55, 1921, p. 310. 46. The Des Plaines River A.S. Plant, by Pearse. E.N.R. V. 88, 1920, p. 1134. 47. Sewage Treatment by the Dorr System, by Eagles. Proceedings, Boston Society of Engineers, 1920. Public Works V. 50, 1920, P. 53. CHAPTER XIX ACID PRECIPITATION, LIME AND ELECTRICITY, AND DISINFECTION 275. The Miles Acid Process. The Miles Acid Process for the treatment of sewage was devised and patented by G. W. Miles. It was tried experimentally at the Calf Pasture sewage pumping station, Boston, Mass., 1911 to 1914. In 1916 it was tried experimentally at the Massachusetts Institute of Tech- nology, and it has been tested subsequently at other places, nota- bly at Ne.w Haven, Conn., in 1917 and 1918. It is one of the most recent developments in sewage treatment and no extensive experience has been had with it. The process consists in the acidification of sewage with sulphuric or sulphurous acid, as the result of which the suspended matter and grease are precipitated and bacteria are removed. The equipment required for the process consists of devices for the production of sulphur dioxide (802), and for feeding niter cake or other forms of acid; sub- siding basins; sludge-handling apparatus; sludge driers; grease extractors; grease stills; and tankage driers and grinders. The first step is the acidification of the sewage. The period of contact with the acid is about 4 hours. Sulphurous acid seems to give better results than sulphuric because of the ease in which it can be manufactured on the spot. It seems also to be more virulent in attacking bacteria than an equal strength of sulphuric acid. Jn experimental plants the acidulation has been accomplished in different ways such as: by the addition of compressed sulphur dioxide from tanks; by the addition of sulphur dioxide made from burning sulphur; or by the roasting of iron pyrite (FeS2). The acidulation precipitates most of the grease as well as the suspended matter and results in a sludge which gives some promise of commercial value. In referring to the process R. S. Weston states: 1 1 Reference 1, at end of this chapter. 482 THE MILES ACID PROCESS 483 (1) It disinfects the sewage by reducing the numbers of bacteria from millions to hundreds per c.c. (2) If the drying of the sludge and the extraction of the grease can be accomplished economically, it is possible that a large part, if not all, of the cost of the acid treat- ment may be met by the sale of the grease and fertilizer recovered from the sewage. (3) The use of so strong a deodorizer and disinfectant as sulphur dioxide would prevent the usual nuisances of treatment works. (4) The addition of sulphur dioxide to the sewage also avoids any fly nuisance, which is a handicap to the operation of Imhoff tanks and trickling filters. The amount of acid used varies with the quality of the sewage and the desired character of the effluent. At Bradford, England, 1 5,500 pounds of sulphuric acid are used per million gallons, producing about 2,340 pounds of grease or 0.43 pound of grease per pound of sulphuric acid. At Boston only 0.215 pound of grease were produced per pound of sulphuric acid. The dif- ference is probably due to the great difference in the amount of grease in the raw sewage. In the East Street sewer at New Haven, Conn., 2 only 700 pounds of acid are used per million gallons of sewage as the alkalinity is only 50 p. p.m. This amount of acid secures an acidity of 50 p.p.m. whereas in the Boulevard sewer 1,130 pounds of acid had to be added to produce the same result. The results obtained by the experiments conducted by the Massachusetts State Board of Health in 1917 are shown in Table 97. The character of the sludge from the same tests is shown in Table 98. After acidification 3 the sewage contains bisulphites and some free sulphurous acid, with some lime and magnesium soaps which are attacked by the acid liberating the free fatty acids. Part of the bisulphites and sulphurous acid are oxidized to bisulphates and sulphuric acid. It was found as a result of the New Haven 3 experiments that the presence of sulphur dioxide in the effluent caused an abnormal oxygen demand from the diluting water and that this difficulty could be partly overcome by the aeration of the effluent after acidulation and sedimentation, without prohibitory expense. The effluent and sludge are both stable for appreciable periods of time and are suitable for disposal by dilution. The character of the 1 Reference 2. 2 Reference 6. 3 Reference 5. 484 ACIDIFICATION, ELECTROLYSIS, DISINFECTION sludge as determined by the New Haven tests l is shown in Table 99. TABLE 97 AVERAGE ANALYSIS OF SEWAGE ENTERING BOSTON HARBOR, BEFORE AND AFTER TREATMENT, JULY 17 TO SEPTEMBER 27, 19i7 (Eng. News-Record, Vol. 80, p. 319) Sample Parts per Million Bacteria, Millions Ammonia Kjeldahl Nitrogen Chlor- ine Oxy- gen Con- sumed Free Albuminoid Total Total Diss. Total Diss. 20 37 Paddock's Island Raw sewage 14.0 '12.2 20.9 3.3 1.6 5.2 1.8 1.1 3.9 6.8 3.5 10.0 3.6 2.2 7.5 134 23.1 15.4 1.86 units 94 4.15 units 91 Settled sewage Acidified and settled sewage Deer Island Raw sewage 23.3 21.1 20.9 8.2 5.6 5.2 4.8 3.9 3.9 16.8 10.7 10.0 8.9 7.3 7.5 3100 87.3 62.2 2.63 units 147 1.50 units 85 Settled sewage Acidified and settled Calf Pasture Raw sewage 18.0 4.5 2.0 9.7 4.1 3254 41.2 1.89 0.98 Settled sewage 19.1 2.3 1.4 4.9 3.3 25.8 Acidified and settled units units 17 8 2.4 1 6 4.9 3.3 277 149 The success of the Miles Acid Process in comparison with other processes is dependent on the commercial value of the sludge produced. The New Haven experiments indicate that 16 to 21 per cent of the grease in the sludge is unsaponifiable and seri- ously impairs the value of the process. 1 Reference 6. THE MILES ACID PROCESS 485 TABLE 98 AVERAGE AMOUNT OF SLUDGE AND FATS OBTAINED FROM SEWAGE ENTER- ING BOSTON HARBOR AFTER EIGHTEEN HOURS SEDIMENTATION WITH AND WITHOUT ACIDIFICATION (Eng. News-Record, Vol. 80, p. 319) Paddock's Island Deer Island Calf Pasture Sedimentation Sedimentation Sedimentation Plain Acidu- lated Plain Acidu- lated Plain Acidu- lated Pounds of SOa used per million gallons of sewage treated .... Dry sludge per million gallons. . Per cent Nitrogen in sludge. . . . Per cent fats in sludge 762 3.10 27.30 818 959 3.38 27.30 1709 3.57 24.60 1513 1939 3.45 19.40 1189 1427 2.83 26.30 1208 3.18 24.30 TABLE 99 CHARACTER OF MILES ACID SLUDGE AT NEW HAVEN (Eng. News-Record, Vol. 81, p. 1034) East Stre ;et Sewer Boule- vard Sewer Length of run in days 25 24 44 70 29 Total sewage treated, thou- sand gallons 260 239.4 407.8 602.2 145.5 Gallons wet sludge per mil- lion gallons sewage 3750 4025 3200 2600 5375 Specific gravity 1.067 1.048 1.054 1.061 Per cent moisture 86.6 88 86.3 85.7 92.5 Pounds of dry sludge per million gallons sewage 503 483 439 368 403 Ether extract, per cent dry sludge 23.7 24.0 29 32.6 30.9 Ether extract, pounds per million gallons . 119 116 127 120 124 Volatile matter, per cent dry sludge 47.2 51.2 57.3 63.8 78.5 Nitrogen, per cent dry sludge 1.6 1.6 2.4 2.0 3.0 486 ACIDIFICATION, ELECTROLYSIS, DISINFECTION The conclusions reached as a result of the New Haven experi- ments are: 1 Our experience with New Haven sewage lends no color to the hope that a net financial profit can be obtained by the use of the Miles Acid Process, except with sewage of exceptionally high grease content and low alkalinity. They do, however, suggest that for communities where clarification and disinfection are desirable where screening would be insufficient and nitrification unnecessary the process of acid treatment comes fairly into competition with the other processes of tank treatment, and that it is particularly suited to dealing with sewages that contain industrial wastes, and to use in localities where local nuisances must be avoided at all costs and where sludge disposal could be provided for only with difficulty. The conclusions reached as a result of the Chicago experi- ments are: 2 The results on hand indicate that treatment of this sewage with acid results in a somewhat greater retention of fat. An apparent reduction in the oxygen demand over that resulting from plain sedimentation, while remark- able, is probably not real, being simply due to a retarda- tion of decomposition by the sterilization of the bacteria present, the organic matter being left in solution. . . . However, there appears the added cost of acid treatment and the cost of recovery of the grease, as well as the uncertainty of the price to be received for the grease recovered. v The cost of the treatment is estimated by Dorr to be $18 per million gallons, and the value of the sludge obtained from the Boston sewage as $24 per million gallons, giving a net margin of profit of $6 per million gallons. At New Haven, the total return is estimated at $7.09 per million gallons. Based on the production of sulphur dioxide by burning sulphur (assumed to cost $36 per long ton) and on drying from 85 per cent to 10 per cent moisture with coal assumed to cost $7.50 per ton, it appears that the acid treatment of sewage should be materially cheaper than either the Imhoff treatment or fine screening under the local conditions. A comparison of the cost of the treatment of the East Street and the Boulevard sewage at New Haven 1 Reference 6. 2 Reference 8. THE MILES ACID PROCESS 487 and the Calf Pasture sewage in Boston is given in Table 100. The cost of construction was estimated by Dorr and Weston in 1919 as greater than $15,000 per million gallons of sewage per day capacity. TABLE 100 ESTIMATED COST OF SEWAGE TREATMENT AT NEW HAVEN AND BOSTON BY THREE DIFFERENT PROCESSES Cost in Dollars per Million Gallons Treated (Engineering and Contracting, Vol. 51, p. 510) Miles Acid Process Imhoff Tank and Chlorination Fine Screens and Chlorination East Boule- Calf East Boule- Calf East Boule- Street vard Pasture Street vard Pasture Street vard Tanks and Buildings Int. and Dep 2.47 2.47 2.47 5.28 4.44 4.60 4.60 Acid treatment . . 6.93 10 74 18 65 Drying sludge 2.09 2.04 10.34 Degreasing sludge .... 1.78 1.91 9.12 Redrying tankage. . . . 0.17 0.17 0.10 Superintendence 1.06 2.65 1.06 46 1 15 47 1 15 Labor on tanks and screens 1.00 1.00 1.00 1.20 1.50 1.42 2.05 Disposal of sludge or screenings 1 00 1.00 50 50 Chlorination 4.05 4.05 4.05 4 05 Gross cost 15.50 20.98 42.75 11.99 12.14 11.03 12.35 6 57 10 66 47 59 Net cost 8 93 10 32 4 84 11 99 12 14 11 03 12 35 I ELECTROLYTIC TREATMENT 276. The Process. This process has been generally unsuc- cessful in the treatment of sewage and has grown into disrepute. In the words of the editor of the Engineering News-Record: 1 Thirty years of experiments and demonstrations with only a few small working plants built and most of them abandoned such in epitome is the record of the electro- lytic process of sewage treatment. It is probably true that the process has never received a thorough and exhaustive test on a large scale, but the small-scale tests have 1 Reference 20. 488 ACIDIFICATION, ELECTROLYSIS, DISINFECTION not been promising of good results. Among the most extensive tests have been those at Elmhurst, Long Island, 1 Decatur, 111., 2 and Easton, Pa. 3 Whatever degree of popularity the method has possessed has been due possibly to the mystery and romance of " elec- tricity " and to the personality of its promoters. The process should, nevertheless, be understood by the engineer in order that it may be explained satisfactorily to the layman interested in its adoption. In this process, sometimes called the direct-oxidation process, all grit is removed and the sewage is passed through fine screens before entering the electrolytic tank. In the electrolytic tank the sewage passes in thin sheets between electrodes and an electric current is discharged through it. A recent develop- ment has been the addition of lime to the sewage at some point in its passage through the electrolytic tank. From the elec- trolytic tank the sewage flows to a sedimentation tank, where sludge is accumulated, and from which the liquid effluent is finally disposed of. It is claimed that the action of the electricity electrolyzes the sewage, releasing chlorine, which acts as a powerful disin- fectant. The constituents of the sewage are oxidized so that the dissolved oxygen, nitrates, and relative stability are increased and the sludge is rendered non-put rescible. It is said that the addition of lime increases the efficiency of sedimentation and enhances the effect of the electric current. The results obtained by tests at Easton, Pa., are shown in Table 101. It will be observed from this table that the combination of lime and electricity does not have a more beneficial effect than either one of them alone. The amount of sludge produced by the com- bination is about the same as by chemical precipitation alone, but the character of the sludge produced with electricity is less putrescible. The cost of the treatment as estimated at Elm- hurst is shown in Table 102. As a result of the tests at Decatur, comparing lime alone with lime and electricity together, Dr. Ed. Bartow stated: The purification by treatment with lime alone was greater than that obtained in several of the individual samples treated with lime and electricity. 1 Reference 17. 2 Reference 19. 3 Reference 21. DISINFECTION OF SEWAGE 489 TABLE 101 COMPARATIVE RESULTS OBTAINED FROM THE TREATMENT OF SEWAGE BY LIME ALONE, ELECTRICITY ALONE, AND LIME AND ELECTRICITY COMBINED (Creighton and Franklin, Journal of the Franklin Institute, August, 1919) Lime and Electricity Lime Alone Electricity Alone Change, Parts Change, Per Change, Parts Change, Per Change, Parts Change, Per per Million Cent per Million Cent per Million Cent Chlorine + 1.2 + 1.9 + 12.3 + 18.2 + 1.6 +2.2 Nitrites +0.014 +58.3 -.005 -10.0 -0.01 -20.0 Nitrates . . . ; +0.13 +23.6 + .005 +0.8 -0.15 -20.0 Ammonia -3.3 -18.3 +0.2 + 1.3 +0.9 +6.6 Albuminoid am- monia -3.6 -12.1 -0.4 -1.7 -0.5 2.3 Oxygen demand. . . -13.0 -20.5 -7.7 -8.9 -6.5 -10.0 Dissolved oxygen . . + 1.78 +40.9 -0.93 -19.1 +1.61 +40.1 Total bacteria at 37 (Thousands) -343 -92.7 -373 -82.4 -165 -37.8 Total bacteria at 20 (Thousands) -688 -92.2 -1074 -90.1 -635 -70.0 B. Coli (Thou- sands) -77.9 -99.85 -96.3 -92 3 -45 -81.8 Oxygen absorbed in 5 days . , -3.40 -81.6 -1.03 -21. +1.24 +31 DISINFECTION 277. Disinfection of Sewage. Sewage is disinfected in order to protect public water supplies, shell fish, and bathing beaches; to prevent the spread of disease; to keep down odors, and to delay putrefaction. Disinfection is the treatment of sewage by which the number of bacteria is greatly reduced. Steriliza- tion is the destruction of all bacterial life, including spores. Ordinarily even the most destructive agents do not accomplish complete sterilization. Chlorine and its compounds are practi- cally the only substances used for the disinfection of sewage. The lime used in chemical precipitation, the acid used in the Miles 490 ACIDIFICATION, ELECTROLYSIS, DISINFECTION Acid Process, the aeration in the activated sludge process, all serve to disinfect sewage, but are not used primarily for that purpose. Copper sulphate has been used as an algaecide but never on a large scale as a bactericide. 1 Heat has been suggested, but its high cost has prevented its practical application to the disinfection of sewage. TABLE 102 COST OF ELECTROLYTIC TREATMENT, ELMHURST, LONG ISLAND, AND EASTON, PENNSYLVANIA Three One Million Gallon Million Gallon Item unit at unit at unit at Easton, Elmhurst, Elmhurst, Dollars Dollars Dollars Hydra ted lime: Elmhurst, 1300 pounds at $7.90 ton. j Easton, 3720 pounds at $6.75 ton. j 12.56 5.14 15.42 Electric power electrolysis: Elmhurst, 85 kw-h. at 4 cents 1 Easton, 185 . 5 kw-h. at 2 . 26 cents j 4.19 3.40 9.60 Electric power, light and agitation: Elmhurst, 60 kw-h. at 4 cents 1 Easton, 6 . 25 kw-h . at 8 . 05 cents J 0.50 2.40 7.20 Heating 1 25 Labor and supervision 15 00 12 50 15 00 Maintenance, repairs and supplies 1.50 1.00 3.00 Sludge pressing and removal 5 11 15 33 Total 35.00 29.55 65 55 Cost per million gallons 35.00 29.55 21.85 The action which takes place on the addition to sewage of chlorine or its compounds is not well understood. The idea that the bacteria are burned up with " nascent " or freshly born oxygen, has been exploded. 2 Likewise the idea that the toxic properties of chlorine have no effect has not been borne out by 1 Reference 24. 2 Inorganic Chemistry, by Alexander Smith. DISINFECTION OF SEWAGE 491 experiments. It has been demonstrated, particularly by tests on strong tannery wastes, that the action of chlorine gas is more effective than the application of the same amount of chlorine in the form of hypochlorite. All that we are certain of at present is that the greater the amount of chlorine added under the same conditions, the greater the bactericidal effect. Chlorine is applied either in the form of a bleaching powder or a gas. In ordinary commercial bleach (calcium hypochlorite) the available chlorine is about 35 to 40 per cent by weight. In order to add one part per million of available chlorine to sewage it is necessary to add about 25 pounds of bleaching powder or 8| pounds of liquid chlorine per million gallons of sewage. This can be computed as follows: The molecular weight of calcium hypochlorite is 127.0. This reacts to produce two atoms of available chlorine with a molecular weight of 70.9. If the bleach- ing powder were pure the available chlorine would there- fore represent 70.9-1-127, or 56 per cent of its weight. Then to obtain one pound of chlorine it would be neces- sary to have 1.79 pounds of pure bleaching powder. Since 1,000,000 gallons of water weigh approximately 8,300,000 pounds, in order to apply one part per million of chlorine to 1,000,000 gallons of sewage it is necessary to apply 1.79X8.3 or 14.9 pounds of pure bleaching powder. Commercial bleaching powder is only about 60 per cent calcium hypochlorite. It is therefore necessary to add 14.9^-0.60 or about 25 pounds of commercial bleach. Since liquid chlorine is very nearly pure, approxi- mately 8| pounds of it applied to 1,000,000 gallons of sewage are equivalent to a dose of one part per million. Commercial bleaching powder is a dry white powder which absorbs moisture slowly, and which loses its strength rapidly when exposed to the air. It is packed in air-tight sheet iron containers, which should be opened under water, or emptied into water immediately on being opened. The strength of the solution should be from i to 1 per cent. The rate of the appli- cation of the solution to the sewage may be controlled by auto- matic feed devices, or by hand-controlled devices. Commercial liquid chlorine is sold in heavy cast steel con- tainers, which hold 100 to 140 pounds of liquid chlorine under a pressure of 54 pounds per square inch at zero degrees C. or 121 pounds per square inch at 20 degrees. 492 ACIDIFICATION, ELECTROLYSIS, DISINFECTION The amount of chlorine used is dependent on the character of the sewage to be treated, the stage of decomposition of the organic matter, the desired degree of disinfection, the period of contact, and the temperature. The amount of chlorine is expressed in parts per million of available chlorine, regardless of the form in which the chlorine is applied. In general about 15 to 20 parts per million of available chlorine with 30 minutes' contact at a temperature of about 15 C. will effect an apparent removal of 99 per cent of the bacteria from the raw sewage. The effect is only apparent because many of the bacteria encased in the solid matter of the sewage escape the effect cf the chlo- rine, or detection in the bacterial analysis. Stronger and older sewages, higher temperatures, and shorter periods of contact will demand more chlorine to produce the same results. A septic effluent will require more chlorine than a raw sewage because of the greater oxygen demand by the septic sewage. The results of experiments on disinfection made at different testing stations have shown such wide variations in the amount of chlorine necessary, as to demonstrate the necessity for inde- pendent studies of any particular sewage which is to be chlori- nated. For instance, at Milwaukee approximately 13 p.p.m. of available chlorine applied to an Imhoff tank effluent effected a 99 per cent removal of bacteria, whereas the same result was obtained at Lawrence, Mass., on crude sewage with only 6.6 p.p.m. and at Marion, Ohio, only 9 per cent removal of bacteria was obtained by the addition of 4,815 p.p.m. to crude sewage. The Ohio and Massachusetts reports show irrational variations among themselves. For instance, 6.2 p.p.m. applied to a septic effluent effected 88 per cent removal whereas in another case 7.6 p.p.m. effected only 36 per cent removal. At Lawrence in one case it took 8.6 p.p.m. to remove 99 per cent from a sand filter effluent, but only 6.3 p.p.m. to effect the same result in the effluent from a septic tank. The most consistent results are those found at Milwaukee which show a steadily increasing percentage removal with increasing amounts of chlorine. Some time after sewage has received its dose of chlorine the number of bacteria may be greater than in the raw* sewage. Such bacteria are called after-growths. Certain forms of bac- teria, particularly the pathogenic or body temperature types, are most susceptible to disinfecting agents. These are killed REFERENCES 493 ( off and leave the sewage in a condition more favorable to the growth of more resistant forms of bacteria. As the latter are non-pathogenic and are generally aerobic their presence is usually more beneficial than detrimental, as they hasten the action of self-purification, REFERENCES The following abbreviations will be used: E.G. for Engineering and Contracting, E.N. for Engineering News, E.R. for Engineering Record, E.N.R. for Engineering News-Record, M.J. for Municipal Journal, p. for page, and V. for volume. No. 1. Grease and Fertilizer Base for Boston Sewage, by Weston, E.N. V. 75, 1916, p. 913 and Journal American Public Health Association, April, 1916. 2. Getting Grease and Fertilizer from City Sewage, by Allen. E.N. V. 75, 1916, p. 1005. 3. New Haven Tests Five Processes of Sewage Treatment. E.N.R. V. 79, 1917, p. 829. 4. Recovery of Grease and Fertilizer from Sewage Comes to the Front. E.N.R. V. 80, 1916, p. 319. 5. Miles Acid Process may Require Aeration of Effluent, by Mohlman. E.N.R. V. 81, 1918, p. 235. 6. Promising Results with Miles Acid Process in New Haven Tests. * E.N.R. V. 81, 1918, p. 1034. 7. Baltimore Experiments on Grease from Sewage. E.N. V. 75, 1916, p. 1155. 8. Report on Industrial Wastes from the Stock Yards and Packingtown in Chicago to the Trustees of the Sanitary District of Chicago, 1914, pp. 187-195. 9. The Separation of Grease from Sewage, by Daniels and Rosenfeld. Cornell Civil Engineer. V. 24, p. 13. 10. The Separation of Grease from Sewage Sludge with Special Reference to Plants and Methods Employed at Bradford and Oldham, England, by Allen. E.G. V. 40, 1913, p. 611. 11. Acid Treatment of Sewage, by Dorr and Weston. Journal Boston Society of Civil Engineers, April, 1919. E.G. V. 51, 1919, p. 510. M. J. V. 46, 1919, p. 365. 12. The Miles Acid Process for Sewage Disposal. Metallurgical and Chemical Engineering, V. 18, p. 591. 13. Miles Acid Treatment of Sewage, by Winslow and Mohlman. Journal American Society Municipal Improvements, Oct., 1918. M. J. V. 45, 1918, pp. 280, 297, and 321. 14. New Electrolytic Sewage Treatment. M.J. V. 37, 1914, p. 556. 494 ACIDIFICATION, ELECTROLYSIS DISINFECTION No. 15. Electrolytic Sewage Treatment. M.J. V. 47, 1919, p. 131. 16. Electrolytic Treatment of Sewage at Durant, Oklahoma, by Benham. E.N. V. 76, 1916, p. 547. Municipal Engineering, V. 49, 1916, p. 141. 17. Electrolytic Treatment of Sewage at Elmhurst, Long Island, by Travis. Report to the President of the Borough of Queens, Aug. 31, 1914. E.R. V. 70, 1914, pp. 292, 315, and 429. M.J. V. 39, p. 551. Muni- cipal Engineering, V. 47, p. 281. 18. Tests of the Electrolysis of Sewage at Toronto, by Nevitt. E.N. V. 71, 1914, p. 1076. 19. Electrolytic Treatment of Sewage Little Better than Lime Alone, by Bartow. E.R. V. 74, 1916, p. 596. 20. Electrolytic Sewage Treatment Not Yet an Established Process. E.N.R. V. 83, 1919, p. 541. 21. Tests of Electrolytic Sewage Treatment Process at Easton, Pa. Journal of the Franklin Institute, Aug., 1919. E.N.R. V. 83, 1919, p. 569. 22. The Disinfection of Sewage. U. S. Geological Survey, Water Supply Paper, No. 229. 23. Sewage Disinfection in Actual Practice, by Orchard. E.R. V. 70, 1914, p. 164. 24. Water and Sewage Purification in Ohio. Report of the Ohio State Board of Health, 1908, pp. 738-762. 25. Water Purification, by Ellms. Published in 1917 by McGraw-Hill Book Co. 26. Electrolytic Sewage Treatment, A Half Century of Invention and Promotion. E.N.'R. V. 86, 1921, p. 25. CHAPTER XX / SLUDGE 278. Methods of Disposal. Sludge is the deposited suspended matter which accumulates as the result of the sedimentation of sewage. The methods for the disposal of sludge as discussed herein will include the disposal of scum. Scum is a floating mass of sewage solids buoyed up in part by entrained gas or grease, forming a greasy mat which remains on the surface of the sewage. 1 The sludges formed by different methods of sewage treatment are described in the chapter devoted to the particular method. The disposal of sludge is a problem common to all methods of sewage treatment involving the use of sedimentation tanks. Sludge is disposed of by: dilution, burial, lagooning, burning, filling land, and as a fertilizer or fertilizer base. Certain methods of disposal, such as burning or as a fertilizer, demand that the sludge be dried preparatory to disposal. Sludge is dried on dry- ing beds, in a centrifuge, in a press, in a hot-air dryer, or by acid precipitation. 279. Lagooning. This is a method of sludge disposal in which fresh sludge is run on to previously prepared beds to a depth of 12 to 18 inches or more, and allowed to stand without further attention. The preparation of the lagoons requires leveling the ground, building of embankments, and, if the ground is not porous, the placing of underdrains laid in sand or gravel. At Reading, Pa., 2 approximately one acre was required for 1,700 cubic yards of wet sludge. The results of lagooning at Philadelphia are given in Table 103. 2 1 American Public Health Association definition. 2 Sewage Sludge by Allen. 495 496 SLUDGE TABLE 103 RESULTS OF DRYING SLUDGE IN LAGOONS AT PHILADELPHIA ("Sewage Sludge" by Allen) Treatment Days Depth, Inches Per Cent, Moisture Rainfall, Inches Cubic Yards per Acre Screened 12.20 82.8 1600 Screened 26 7.67 57 1000 Screened 49 3 50 51 6 43 470 Screened o 13 50 90 1 o 1800 Screened 62 7.00 61 3 14 950 Crude 12 00 88 7 1600 Crude 59 4.70 62.8 2.59 640 During the period of standing in the lagoon the moisture drains out and evaporates and the organic matter putrefies, giving off gases and foul odors. In the course of three to six months, biological action ceases and the sludge has become humified and reduced to about 75 per cent moisture. In the utilization of this method of disposal the lagoons must be removed from settled districts and should occupy land of little value for other purposes. The odors created at the lagoons may be intense and offensive. The land so used is rendered unfit for other pur- poses for many years. The digestion of sludge in special tanks is a form of lagooning in which an attempt is made to maintain septic action as a result of which a portion of the sludge is gasified or liquefied, leaving less to be cared for by some of the other methods of treatment or disposal. The results obtained by digestion tanks has not been entirely satisfactory. A partial drying and consolidation of the sludge may be effected, however, by the process of decanta- tion, in which the supernatant liquid is run off, followed by further sedimentation, rendering the final product more compact. 280. Dilution. In the disposal of sludge by dilution, as in the disposal of sewage by dilution, there must be sufficient oxygen available in the diluting water to prevent putrefaction, and a swift current to prevent sedimentation. Such conditions exist in localities along the sea coast, and in communities DILUTION 497 situated near rivers, when the rivers are in flood. In some sea- coast towns, for example at London and Glasgow, the sludge is taken out to sea in boats, and dumped. Since it is not necessary to discharge sludge continuously, it can be stored to advantage in the digestion chamber of a tank, until the conditions in the body of diluting water are suitable to receive it. The amount of diluting water to receive sewage sludge has not been sufficiently well determined to draw reliable general con- clusions. A dilution of 1,500 to 2,000 volumes may be considered sufficiently safe to avoid a nuisance provided there is a sufficient velocity to prevent sedimentation. Johnson's Report on Sew- age Purification at Columbus, Ohio (1905), states that a dilution of 1 to 800 is sufficient to avoid a nuisance. The character of the sludge has a marked effect on the proper ratio of dilution, the sludge from septic and sedimentation tanks requiring a greater dilution than that from Imhoff tanks. 281. Burial. Sludge can be disposed of by burial in trenches about 24 inches deep with at least 12 inches of earth cover, without causing a nuisance. The ground used for this purpose should be well drained. This method of disposal is generally used as a makeshift and has not been practiced extensively because of the large amount of land required. Insufficient infor- mation is available to generalize on the amount of land required or the time before the land can be used for further sludge burial, or for other purposes. Indications are that the sludge may remain moist and malodorous for years and that the land may be rendered permanently unfit for further sludge burial. Under some conditions the land may be used again for the same or other purposes. For example, Kinnicutt, Winslow and Pratt 1 state that 500 tons of wet sludge can be applied per acre and : The same land, it is claimed, can be used again after a period of a year and a half to two years, if in two months or so after covering the sludge with earth, the ground is broken up, planted, and, when the crop is removed, again plowed and allowed to remain fallow for about a year. 282. Drying. Before sludge can be disposed of to fill land, by burning, or for use as a fertilizer filler it must be dried to a suitable degree of moisture. The removal of moisture from the 1 Sewage Disposal by Kinnicutt, Winslow and Pratt. 498 SLUDGE sludge decreases its volume and changes its characteristics so that sludge containing 75 per cent moisture has lost all the char- acteristics of a liquid. It can be moved with a shovel or fork, and can be transported in non-watertight containers. A reduction in moisture from 95 to 90 per cent will cut the volume in half. The change in volume on the removal of moisture can be represented as: _ 7(100- P) ~ (100- Pi) 7 in which P = the original percentage of moisture; PI = the final percentage of moisture; F=the original volume; Vi = the final volume. The drying of sludge on coarse sand filter beds is more particularly suited to sludge from Imhoff tanks. This sludge does not decompose during drying, and is sufficiently light and porous in texture to permit of thorough draining. The sludge from plain sedimentation or chemical precipitation tanks is high in moisture, putrescible, and when placed on a filter bed it settles into a heavy, compact, impervious mass which dries slowly. In order to avoid this condition the sludge is run on to the beds as quickly as possible, to a depth of not more than 6 to 10 inches. Lime is sometimes added to the sludge at this time as it aids drying by assisting in the maintenance of the porosity of the sludge, and it is advantageous in keeping down odors and insects. Sludge filter beds are made up of 12 to 24 inches of coarse sand, well-screened cinders, or other gritty material, underlaid by 6 inches of coarse gravel and 6 or 8-inch open-joint tile underdrains, laid 4 to 10 feet apart on centers, dependent on the porosity of the subsoil. The side walls of the filters are made of planks or of low earth embankments. The sludge filters at Hamilton, Ontario, are shown in Fig. 179. The size of the bed is dependent mainly upon the character- istics of the sludge. For Imhoff tank sludge which comes from the tank with about 85 per cent moisture, the practice is to allow about 350 1 square feet of filter surface per 1,000 popu- 1 Sewage Disposal by Fuller. DRYING 499 lation contributing sludge. For other types of sludge the area varies from 900 to 9,000 square foot per 1,000 population con- tributing sludge, and only experiments with the sludge in hand can determine the proper allowance. Imhoff recommends 1,080 ^8" C.I. Sludge Pipe, Part Plan, r Part Cross Section A-B, FIG. 179. Sludge-drying Beds at Hamilton, Ontario. Eng. News, Vol. 73, p. 426, square feet per 1,000 population for septic tank sludge, and 6,480 square feet for sludge from plain sedimentation tanks. 1 Kinnicutt, Winslow, and Pratt in their book on Sewage Disposal state : With an average depth of 10 inches per dose of sludge of 87 per cent water content, one square foot of covered (glass) bed should dry to a spadable condition one cubic yard of sludge per year. Sewage Sludge by Allen. 500 SLUDGE The sludge is run on the bed in small quantities at periods from two weeks to a month apart. In favorable weather Imhoff sludge will dry in two weeks or less to approximately 50 to 60 per cent moisture. It is then suitable for use as a filling material on waste land, for burning, or for further drying by heat. Glass roofs, similar to those used on green-houses, have been used to speed the drying process by preventing the moistening of partly dried sludge during rainy weather. In some instances sludge has dried to 10 per cent moisture on such beds. Imhoff sludge can be removed from the drying beds with a manure or hay fork. It has an odor similar to well-fertilized garden soil. It is stable, dark brownish-gray in color, is of light coarse material, and is granular in texture. Sludge presses are suitable for removing moisture from the bulky wet sludge obtained from plain sedimentation, chemical precipitation, and the activated sludge process. The details of a typical sludge press are shown in Fig. 180. The press shown is made up of a number of corrugated metal plates about 30 inches in diameter with a hole in the center about 8 inches in diameter. The corrugations run vertically except for a distance about 3 inches wide around the outer rim, which is smooth. To this smooth portion is fastened, on each side of the plate, an annular ring about an inch thick and 2 to 3 inches wide, of the same outside diameter as the plate. A circular piece of burlap, canvas, or other heavy cloth is fastened to this ring, covering the plate completely. A hole is cut in the center of the cloth slightly smaller in diameter than the center hole in the plate, and the edges of the cloth on opposite sides of the plate are sewed together. The plates are then pressed tightly together by means of the screw motion at the left end of the machine, thus making a water-tight joint at the outer rim. Sludge is then forced under pressure into the space between the plates, passing through the machine by means of the central hole. The pressure ori the sludge may be from 50 to 100 pounds per square inch. This pressure forces the water out of the sludge through the porous cloth from which it escapes to the bottom of the press along the corrugations of the sepa- rating plate. After a period of 10 to 30 minutes the pressure is released, the cells are opened, and the moist sludge cake is DRYING 501 removed. The liquid pressed from the sludge is highly putres- cible and should be returned to the influent of the treatment plant. The pressing of wet greasy sludges is facilitated by the addition of from 8 to 10 pounds of lime per cubic yard of sludge. The cake thus formed is more cohesive and easy to handle. The output of the press depends so much on the character of the sludge that a definite guarantee of capacity is seldom given by the manufacturer. The simplest form of centrifugal sludge dryer is a machine which consists of a perforated metal bowl lined with porous cloth in which the sludge is placed. Surrounding this bowl is FIG. 180. Filter Press. a second water-tight metal bowl so arranged as to intercept the water thrown from the sides of the inner bowl as it revolves. The peripheral velocity of the inner bowl is about 6,000 feet per minute, which makes the effective weight, of each particle about 250 times its normal weight when at rest. Very few data are available on the operation of such machines, and their use has not been extensive because of the difficulty of starting and stopping the machine at each filling, and the difficulty of removing the partially dried sludge from the inner basket. The Besco- ter-Meer centrifuge, manufactured by the Earth Engineering and Sanitation Co., can be operated continuously and the diffi- culties of removing the dried sludge from the machine have 502 SLUDGE been overcome. According to the manufacturers the centri- fuge has been operated very successfully in Germany on plain septic tank sludge. A removal of 70 per cent of suspended solids in the raw sludge and a production of 3,600 pounds of sludge per hour, containing 60 to 70 per cent of moisture, can be obtained at less than 900 r.p.m. with a consumption of 15 horse-power. Extensive tests of the machine were made at Milwaukee from October, 1920, to September, 1921, on activated sludge, Besco-ter-Meer Sludge Drying Centrifuge at Milwaukee, Wisconsin Courtesy, Barth Engineering and Sanitation Co. but results of these tests are not as yet available. Indications are that the centrifuge has acted as a classifier. The coarser particles of sludge have been removed but the finer particles have been continuously returned with the liquid to the sedimentation tank, ultimately filling this tank with fine particles of sludge. An illustration of the unit tested at Mil- waukee is shown on this page. DRYING 503 Experiments on the drying of sludge by acid flotation have not progressed sufficiently to allow the installation of a working unit. The method, which has been applied principally to activated sludge, consists in adding a small amount of sulphuric acid to the sludge as it leaves the storage tank. The sludge is coagulated by this action, the coagulated material rising to the surface as a scum containing about 86 per cent moisture. The consistency is such that it can be removed with a shovel. The liquid can be withdrawn continuously from below the scum. The moisture content of sludge to be used in the manufacture of fertilizer must be reduced to 10 per cent or less. None of FIG. 181. Direct-Indirect Sludge Dryer. Courtesy, the Buckeye Dryer Co. the methods of drying described so far can be relied upon for such a product and it becomes necessary to use direct or indirect heat dryers. There are various types of dryers on the market. The details of a Buckeye dryer are shown in Fig. 181. In the operation of this machine moist sludge is fed in at the left end at the point marked "feed." The hot gases pass from the fire box up and around the cylinder which revolves at about eight r.p.m. The gases are drawn into the inner cylinder through the open- ings marked A which revolve with the two cylinders. The gases escape from the inner cylinder through the openings to the right and flow towards the left in the outer cylinder, They come 504 SLUDGE in contact with the sludge at this point. The gases then pass off through the fan at the left. The sludge is lifted by the small longitudinal baffles fastened to the outer cylinder, as the drying cylinders revolve. The right end of the cylinder is placed lower than the left so that the drying sludge is lifted and dropped through the cylinder at the same time that it moves slowly toward the right-hand end of the cylinder. These dryers require about one pound of fuel for 10 pounds of water evaporated. The odors from the dryer can be suppressed by passing the gases through a dust chamber and washer. A summary of the results from methods of sludge drying at Milwaukee 1 follows: Excess sludge produced, 12,100 gallons, having 97.5 per cent moisture, per million gallons of sewage treated. Sludge cake produced (by presses), 10,083 pounds having. 80.3 per cent moisture, per million gallons of sewage treated. Dried sludge (from heat driers) produced, 2,521 pounds having 10 per cent moisture, per million gallons of sewage treated. Press will produce 3 pounds of cake per square foot of filter cloth in four and a half hours, or five operations per twenty-four hours. Dryers will reduce 6,700 pounds of sludge cake at 80 per cent moisture to 10 per cent moisture, and will evaporate 8 pounds of water per pound of combustible. x * Thickening devices known as Dorr thickeners, patented and manufactured by the Dorr Co. and originally intended for metallurgical purposes, have been adapted to the thickening of sewage sludge. These thickeners are circular sedimentation tanks, from 8 to 12 feet deep, more or less, and are made in any diameter up to 200 feet or more. An arm, pivoted in the center and extending to the circumference, is provided at the bottom with a number of baffles or squeegees set at an angle with the arm. The arm revolves at from one to fifteen revolutions per hour, and the squeegees, in contact with the bottom of the tank, scrape the deposited sludge towards a central sump, from which 1 From Eng. News-Record, Vol. 84, 1920, p. 995. DRYING 505 / it is removed by a pump or by gravity, without interrupting the operation of the thickener. The sludge so thickened may be reduced to 95 or 96 per cent moisture. These devices are ordi- narily used only in the activated sludge process in which they have been a pronounced success. CHAPTER XXI AUTOMATIC DOSING DEVICES 283. Types. Automatic dosing devices are used to apply sewage to contact beds, trickling filters, and intermittent sand filters. These devices can be separated into two classes; those with moving parts and those without moving parts. The latter are better known as air-locked dosing devices. Simple devices without moving parts are less liable to disorders and are nearer " fool-proof " than any device depending on moving parts for its operation. No one type of moving part device has been used extensively in different sewage treatment plants. Designing engineers have exercised their ingenuity at different plants, resulting in the production of different types. 1 Among the best known forms is the apparatus designed by J. W. Alvord for the intermittent sand filters at Lake Forest, Illinois. 2 In its operation. , , , A float in the dosing chamber lifts an iron ball in one of a series of wooden columns, and at a certain height the ball rolls through a trough from one column to the next, in its passage striking a catch, which opens an air valve attached to one of ten bell-siphons in the dosing chamber. Each of the siphons discharges on one of the ten sand beds, which are thus dosed in rotation, Since air-locked dosing devices are in more general use their operation will be explained in greater detail. 284. Operation. The simplest form of these devices is the automatic siphon used for flush-tanks, the operation of which is described in Art. 61. In the operation of sand filters, sprinkling filters, or other forms of treatment where there are two or more units to be dosed 1 A Simple Mechanical Control for Dosing Sewage Beds, by P. Thompson, Eng. News-Record, Vol. 84, 1920, p. 1018. 2 Sewage Disposal by Kinnicutt, Winslow and Pratt. 506 OPERATION 507 it is desirable that the dosing of the beds be done alternately. A simple arrangement for two siphons operating alternately is shown in Fig. 182. They operate as follows: with the dosing tank empty at the start water will stand at W in siphon No. 2 and at aa' in siphon No. 1. As the water enters through the inlet on the left the tank fills. When the water rises sufficiently, air is trapped in the bells, and as the water continues to rise in the tank, surfaces a and b are depressed an equal amount. When b has been depressed to d, a has been depressed to c. Air is released from siphon No. 2 through the short leg, and siphon Inlet No. I No.. 2 Plan, : * v : ! 1(11 ff"s] ^ i if si ; i i \ \ ^ ' 1 I)- m o Q V% ^5/7 *^? Section . ^ A-A VV^ Dosing Tank Pipe FIG. 182. Diagram Showing the Operation of Two Alternating Siphons. No. 2 goes into operation. Surface c rises in siphon No. 1 as the tank empties and when the action of Siphon No. 2 is broken by the admission of air when the bottom of the bell is uncovered the water in siphon No. 1 has assumed the position of W and that in No. 2 is at aa'. The conditions of the two siphons are now reversed from that at the beginning of the operation and as the tank refills siphon No. 1 will go into operation. It is to be noted that these siphons are made to alternate by weakening the seal of the next one to discharge and by strengthening the seal of the one which has just discharged. 508 AUTOMATIC DOSING DEVICES 285. Three Alternating Siphons. This principle can be extended to the operation of three alternating siphons as shown in Fig. No. 183. These operate as follows: with the dosing tank empty at the start and water at aa r in siphons 1 and 2, and at bb' in siphon No. 3, the dosing tank will be allowed to fill. As the water rises in the tank air is trapped in all the bells and surfaces a and b are depressed. When surface 6 has been depressed to d, a has been depressed to c. Air is released from siphon No. 3 and this siphon goes into action. Surface c rises Inlet No. I No,? Plan FIG. 183. Diagram Showing the Operation of Three Alternating Siphons. in siphons 1 and 2 to the position 6, as the dosing tank is emptied. At the same time a small amount of water is passed from siphon No. 3 to the short leg of siphon No. 1, through the small pipes shown, thus filling this leg so that when siphon No. 3 ceases to operate the water in siphons 1 and 3 stands at aa' and that in No. 2 stands at bb'. Siphon No. 2, having the weaker seal, will be the next to operate. During its operation it will fill siphon No. 3, leaving No. 1 weak. When No. 1 operates it will refill No. 2, leaving No. 3 weak, thus completing a cycle for the three siphons. This principle has not been applied to the operation FOUR OR MORE ALTERNATING SIPHONS 509 of more than three alternating siphons and is seldom used on recent installations. 286. Four or More Alternating Siphons. An arrangement for the alternation of four or more siphons is illustrated in Fig. 184. At the commencement of the cycle it will be assumed that all starting wells are filled with water except well No. 1, and that all main and all blow-off traps are filled with water. The following FIG. 184. Miller Plural Alternating Siphons. Courtesy, Pacific Flush Tank Co. description of the operation of the siphons is taken from the catalog of the Pacific Flush Tank Company : The liquid in the tank gradually rises and finally overflows into the starting well No. 1 and the starting bell being filled with air, pressure is developed which is transm tted, as shown by the arrows, to the blow-off trap connected with siphon No. 2. When the discharge line is reached, sufficient head is obtained on the starting bell to force the seal in blow-off trap No. 2, thus releasing the air confined in siphon No. 2 and bringing it into full operation. 510 AUTOMATIC DOSING DEVICES During the time that siphon No. 2 ,. is operating, siphonic action is developed in the draining siphon con- nected with starting well No. 2 and as soon as the level in the tank is below the top of the well it is drained down to a point below the bottom of starting well No. 2. It can now be seen that after the first discharge starting well No. 2 is empty, whereas the other three are full. . . . There- fore when the tank is filled the second time, pressure is developed in starting bell No. 2, which forces the seal of blow-off trap No 3, thus starting siphon No. 3. ... This alternation can be continued for any number of siphons. Other arrangements have been devised for the automatic con- trol of alternating siphons, but these principles of the air-locked devices are fundamental. 287. Timed Siphons. In the operation of a number of contact beds not only must the dosing of the tanks be alternated , but some method is needed by which the beds shall be automat- ically emptied after the proper period of standing full. To fulfill this need the principle of the timed siphon must be employed in conjunction with the alternating siphons. Fig. 185 illustrates the operation of the Miller timed siphon. Its operation is as follows: water is admitted to the contact bed and transmitted to the main siphon chamber through the " opening into bed." Water flows from the main siphon chamber into the timing chamber at a rate determined by the timing valve. The con- tact bed is held full during this period. As the timing chamber fills with water air is caught in the starting bell and the pressure is increased until the seal in the main blow-off trap is blown and the main siphon is put into operation. As the water level in the main siphon chamber descends, water flows from the timing chamber into the main siphon through the draining siphon and the tuning chamber is emptied, ready to commence another cycle. 288. Multiple Alternating and Timed Siphons. 1 The alter- nating and timing of a number of beds is more complicated. The arrangement necessary for this is shown in Fig. 186. It will be assumed at the start that all beds are empty and that all feeds are air locked as shown in Section A B except that to bed No. 4 into which sewage is running. As bed No. 4 fills, sewage 1 Design of Siphon by G. H. Bayles, Eng. News-Record, Vol. 84, 1920, p. 974. MULTIPLE ALTERNATING AND TIMED SIPHONS 511 is transmitted through the opening in the wall into the timed siphon chamber No. 4. When the level of 'the water in the bed and therefore in this chamber has reached the top of the with- draw siphon leading to the compression dome chamber No. 4, this latter chamber is quickly filled. The air pressure in starting bell No. 4a is transmitted to blow-off trap No. la. The seal of this trap is blown, releasing the air lock in feed No. 1 and the Contact Bed Air Vent Is not necessary where Siphon discharges info an open Carrier, or Outlet is not more than 50 feet away. FIG. 185. Miller Timed Siphon. Courtesy, Pacific Flush Tank Co. flow into bed No. 1 is commenced. At the same time the air pressure in compression dome No. 4 is transmitted to feed No. 4, air locking this feed and stopping the flow into bed No. 4. The alternation of the feed into the different beds is continued in this manner. Bed No. 4 is now standing full and No. 1 is filling. When compression dome chamber No. 4 was filled, water started flowing through timing siphon valve No. 4 into timing chamber 512 AUTOMATIC DOSING DEVICES No. 4 at a rate determined by the amount of the opening of the timing valve. As this chamber fills compression is transmitted to blow-off trap 46 and when sufficiently great this trap is blown and timed siphon No. 4 is put into operation. Bed No. 4 is emptied by it, and compression dome chamber No. 4 is emptied C.LMei Marring Bell No.4 a. -Inlet Blow-off Trap No. la Bed No. I "Blow-off Trap FIG. 186. Plural Timed and Alternating Siphons for Contact Bed Control. Courtesy, Pacific Flush Tank Co. through the withdraw siphon at the same time. This com- pletes a cycle for the filling and emptying of one bed and the method of passing the dose on to another bed has been explained. The principle can be extended to the operation of any number of beds. INDEX A. B. C. process of sewage treat- ment, 4 Abandonment of contract, 225 Access to work, 228, 229 Accident, contractor's responsibility, 221, 224 Acetylene, explosive, 347 Acid precipitation. See Miles Acid Process. of sludge, 503 Acids as disinfectants, 489, 490. Activated sludge. Chapter XVIII, 465^79 advantages and disadvantages, 469, 470 aeration tank, 471, 472 air diffusion, 475, 477 air distribution, 473-478 air quantity, 475, 476 area of filtros plates, 478 colloid removal, 358 composition, 465-469 cost, 478, 479 definition, 466 dewatering, 468, 469, 497-505 fertilizing value, 469, 470 historical, 470, 471 how obtained, 478 nitrogen content, 468 patent, 471 process, 465 quantity, 469 reaeration tank, 473 results, 467, 468, 476 sedimentation tank, 472 Advertisement, 214 Aeration, effect on oxygen dissolved, 373-375 of sewage, 371, 376, 465-479 Aerobes, 363 Aerobic decomposition, 366, 367 Aftergrowths, 492 Aggregates, specifications, 172-174 Air, see also ventilation, activated sludge, compressed air, etc. ejectors, 150 lock dosing apparatus. Chap. XXI, 506-512 machinery for activated sludge, 473, 474 Algae, 363 Alkalinity, 358 Alleys, sewers in, 80 Alum, 407, 408 Alvord tank, 427, 429 Ammonia, 366, 367, 374, 375, 410 explosives, 297 Analyses, bacteriological, 364 chemical, 354, 355 mechanical of sand, 182 physical, 352-354 sewage, 352-364 Anerobes, 363, 365-367 Anaerobic, action, 410 bacteria, 363 conditions, 367 decomposition, 365-367 Ann Arbor, Michigan. Population, 14 Annual expense, method of financing, 157, 158 Ansonia air ejector, 150, 151 513 514 INDEX Antibiosis, definition, 363 Appurtenances to sewers. Chap. VI, 99-115 Arch, analyses, 204-208 elastic method, 206-208 vouissoir analysis, 204-206 brick construction, 312, 313 centers for brick sewers, 313 concrete construction, 318-321 Ardern and Lockett, development of activated sludge, 467, 468, 471 Area of cities, 31 Asphyxiation in sewer gas, 336 Assessments, special, 15, 16 Augers, earth, 21 Automatic, regulators, 117-121 siphons, flush tanks, 110 double alternating, 507 multiple alternating, 508-512 timed, 510 timed and multiple alternating, 510-512 triple alternating, 508 Bacillus, definition and morphology, 362, 363 Backfilling, 328-331 Backfill, puddling, 330 weight of, 199, 201 Backwater curve, 73 Bacteria, definition and morphology, 362, 363 good and bad, 363, 364 nature of, 362, 363 nitrifying, 431, 432 sanitary significance of, 364 in sewage, 362, 363 total count, 364 Bacterial analyses, results in sewage, 364 Baffles, scum, 404, 413, 414, 421 in sedimentation tanks, 404 in septic tanks, 413, 414 in Imhoff tanks, 421 Balls, for cleaning sewers, 338 Band screen, 384 Barring, definition, 263 Bars for screens, 390 Basins, sedimentation, baffling, 404 bottoms, 404 cleaning arrangements, 404 depth, 401 economical dimensions, 401-403 inlets and outlets, 404 scum boards, 404 types, 395 Basket handle sewer section, 67, 69 Bathing beaches, pollution, 381 Bazin's formula, 54 Bearings, for centrifugal pumps, 131, 137, 138 thrust, 138 Bellmouth, 121, 122 Bends in pipe, loss of head in, 116 Berlin, sewage farm, 460, 461 sewers, date of, 3 Bids, proposal, 217-219 Bidder's duties, 215-217 Bio-chemical oxygen demand, 359 361 Biolysis of sewage, 366, 367 Black and Phelps dilution formulas, 377-379 Blasting and explosives, 294-304 caps, 297, 299, 300 detonators, 294, 297-300 firing, 302-304 fuses and detonators, 297-300 fuses, delayed action, 291, 300 fuses, electric, 299, 300 splicing, 303 gelatine, 296 loading holes, 303 powder, 295 precautions, 300-302 priming and loading, 303 rock, 269 size of charge, 304, 305 tunneling, 290, 291 Bleach, characteristics of for dis- infection, 491 Block sewer, construction, 311-314 hollow tile as underdrains, 126 Blocks, vitrified clay, 189, 190 Boilers, steam, 147-150 INDEX 513 Boilers, efficiencies, 149 horse-power, 149 Bond, contractor's, 213, 214, 232 issues, 14 Bonds, definition and types, 14-16 Boring underground, 20 Bottom, activated sludge aeration tank, 472 Imhoff tanks, 423 sedimentation tanks, 404 trickling filter, 451, 452 Box sheeting, 272 Branch sewer, defined, 7 Breast boards, 288 Brick, arch construction, 312, 313 and block sewer construction, 311- 315 invert construction, 311, 312 sewer construction, 311-315 arch centers, 313 invert, 311-312 organization, 314, 315 progress, 314 row lock bond, 312 specifications, 188, 189 sewers, life of, 351 Bricks for sewers, 316 British Royal Commission on Sewage Disposal, 4 Broad irrigation. See under Irriga- tion. Bucket excavators, 246, 255, 256 Building material, weight of, 201 Burkli-Ziegler formula, 47, 425 Butryn, 366 Cableway excavators, 246, 250-252 Cage screen, 384, 385 Caisson excavation, 285, 286 Calcium carbide, explosive, 347 Calumet pumping station, 128, 142 Cameron septic patent, 411 Capacity of sewers, diagrams, 57-60 Capital, private invested in sewers, 17 Capitalization, method of financing, 157-160 Caps, blasting. See blasting. Carbohydrate, 366, 367 Carbon, analysis for, 356 dioxide, 366, 367 Carson Trench machine, 250, 251 Cast-iron pipe, 122, 164, 190, 191 joints, 164 quality, 101, 102, 190 Castings, iron, 101, 102 Catch-basins, 99, 107-108, 217 cleaning, 343, 344 inspection, 337 Catenary sewer section, 69 Cellars, depth of, 88 Cellulose, 367 Cement. See also Concrete. pipe, specifications, manufacture and sizes, 171-179 vs. concrete, 164 Centrifugal pumps. See pumps, centrifugal. Centrifuge for sludge drying, 501, 502 Cesspool, 411, 416, 417 Champaign, Illinois, septic tank, 415, 416 Changes in plan, 222, 223 Channeling, definition, 263 Character of surface, 44 Chemical analyses, 354-362 Chemical precipitation, 371, 405-409 chemicals used, 405-407 preparation of chemicals, 407, 408 results, 408, 409 at Worcester, 408 Chezy formula, 52, 53 Chicago. See also Sanitary District of Chicago. drainage canal, 374, 375 dilution requirement for sewage, 380 early sewers, 3 method of sewage disposal, 374 population and density, 29, 30 trench excavation in, 248 Chlorine. See also Disinfection. disinfectant, 489-493 in sewage, 358, 374, 375 Chlorine liquid, application, 491, 492 Cholera, transmittable disease, 364 516 INDEX Chromatin, 365 Chutes for concrete, 187 Circular sewer section, hydraulic ele- ments, 65, 66, 69 types, 70, 71 City, growth of area, 31 growth of population, 24-28 legal powers, 219 Clay, life of pipe, 349-351 manufacture of pipe, 165-167 specifications for pipe, 168-170 unglazed for pipe, 165 vitrified blocks, 167, 189, 190 vitrified pipe, 165-171 Cleaning, grit chambers, 398, 400 sedimentation basins, 404 sewers, cost, 341 in N. Y. City, 332 methods, 337-343 tools, 338-340 up after completion of work, 228 Coccus, 362 Coefficient of uniformity of sand, 456 Coffin sewer regulator, 117, 118 Colloid, nature of, 358 treatment for, 358 Color of sewage, 352, 353 Combined sewer system, 78, 79 Commercial districts, characteristics of and sewage from, 32, 34, 35 Compensators for pumps, 142 Compressed air. See also ventilation, tunneling, drilling, etc. activated sludge, 473-475 for drilling, 264-268 in tunnels, 292-294 transporting concrete, 320, 321 Concentration, time of flood flow, 41-43, 96, 97 Concrete, aggregates, 172-174 mixing and placing, 184-188 pipe, details, 175-179 manufacture, 171-179 reinforcement, 177, 178, 209, 210 pipe, steam process, 176 sizes, 175 pressure against forms, 232, 323 Concrete, proportioning, 179-183 qualities, 179, 180 reinforcement, placing, 178, 326, 327 reinforcing steel, quality, 191 sewer construction, 314-328 arch, 318-321 form length, 319 labor costs, 327, 328 in open cut, 314-320 in tunnel, 320, 321 invert, 315-320 organization for, 328 working joints, 319 sewer costs, 327-329 strength, 181 waterproofing, 184 Conduits, special sections, 67, 70, 71 Connections to sewers, ordinances, 344, 345 record of 92, 238 Construction of sewers, Chap. XI, 233-331 Construction, elements of, 233 organizations, 315, 328 Contact bed, 432-437, 506 advantages and disadvantages, 432-434 automatic control, 437, 506 cleaning, 435 clogging, 435 construction, 434-436 control, 437, 506 cycle, 436, 437 depth, 434 description, 432, 433 design, 434-436 dimensions, 434, 435 loss of capacity, 435 material, 435, 436 multiple, 433, 435 operating conditions, 432-437 rate, 435 results, 433, 434 ripening, 432 Continuous bucket excavators, 246- 250 Contour interval on maps, 79, 80 INDEX 517 Contracts, Chap. X, 211-232 abandonment of, 225 assignment, 228 completion of, 222, 228 bond, 213, 222 content, 213, 230, 231 cost-plus, 212, 213 disputes, 220 divisions of, 213 drawings, 213 engineer as an arbitrator, 220 the instrument, 230, 231 interpretation of, 220, 234, 235 lump sum, 212 nature of, 211, 212 sample, 230, 231 time allowed, 222 types, 212, 213 unit price, 213 Contractor, absence of, 222 bond, 232 claims against, 228 duties, 221 liability, 224 relations with other contractors, 228, 229 Contractor's powder, 294 Control devices, automatic, for sew- ers, 117-121 for filters, 506-512 inspection of, 336, 337 Copper sulphate, disinfectant, 490 Copperas, precipitant, 406-408 Cordeau Bickford, 298, 303 Corrugated iron pipe, 165 Cost. See under item wanted. Cost, annual. Method of financing, 157-160 capitalized. Method of financing, 157-160 classification of, 235-238 comparisons of. Methods for making, 157-160 collection of data, 10-14, 235-238 estimate. Method of making, 10-14 overhead, 237, 238 Couplings, flexible for shafts, 138 Covers, Imhoff tanks, 424 septic tanks, 415 trickling filters, 451 Crops on sewage farms, 463,464 Cunette, 67, 70 Cut, depth of excavation, 88, 92. Cycle, contact bed, 436 life and death, 367, 431 nitrogen, 367, 368 trickling filter, 441 Cylinders, stresses in, 194, 202-204 Cytoplasm, 365 Damages, liquidated, 222 material, 221, 224 Darcy's formula, 52 Day labor, 211 Decomposition of sewage, 365-367 Definitions. See word defined. Deflagration, definition, 294 Delays in contract work, 228 Delayed action fuses, 291, 300 Densities. See population. Depreciation, of sewers, 348-351 rate of, financial, 158 Depth of sewers, 88 Design conditions, 88-92 economical, mathematics of, 401- 403 preparations for, 17-23 Detention period, grit chamber, 397 Imhoff tank, 419 plain sedimentation, 392-395, 401 septic tank, 415 Detonation, definition, 294 Detonator. See blasting cap. Diameter of sewers, 57-60, 72, 88- 92 Diaphragm pump, 257, 258 Diesel engine, 152, 154 Digestion chamber, Imhoff tank, 422, 423 Digestion of sludge in separate tank, 427-430, 497 Dilution, amount needed, 377-380 conditions for success, 372, 373 518 INDEX Dilution, definition, 372 formulas for quantity, 378-380 governmental control, 380, 381 preliminary studies, 381, 382 in salt water, 376, 377 in streams, 372-376 of sewage, 370 and Chap. XIV, 372-382 Diseases, water-borne, 364 Disinfection, 489-493 action of, 489-491 bleaching powder, 491 chlorine, liquid, 491 amount of, 492 disinfectants, 489, 490 purpose, 489 selective action of disinfectants, 492, 493 Disk screen, 384 Disposal of sewage, See sewage treat- ment. Disputes, engineer to settle, 220 Dissolved oxygen. See Oxygen dis- solved. Distribution of sewage, contact beds, 436 irrigation, 461, 462 nozzles, 442-449 sand filter, 450-458 traveling distributor, 442 trickling filters, 441-451 Districts, character of, 29, 30, 32-37 classification of, 34, 35 Domestic sewage, defined, 6, 7, 352 Dorr Thickeners, 472, 504 Dortmund tank, 404 Dosing devices, 506-512 alternating and timed siphons, 500-512 Alvord device at Lake Forest, 506 four or more alternating siphons, 509 operation of automatic siphon, 110 three alternating siphons, 508 timed siphons, 510 two alternating siphons, 507 types, 506 Dosing tank design, for trickling filter, 446-450 Doten tank, 429, 430 Drag line excavators, 255, 256 Drainage areas, 81, 84, 94 Drills, electric, 267 jack hammer, 264, 265 punch, 20 size of cylinder for, 266 tripod, 264, 265 Drilling, methods, 20-23, 264-270 depth, diameter and spacing of holes, 268-270 power for, 267, 268 rate of, in rock, 267 steam and air, 267, 268 Drop manhole, 100, 101 Drop-down curve, 73, 77 Drum screen, 384 Dry-weather flow, 24, 38 Drying sludge. See sludge drying. Dualin, 296 Duty of contractor. See Contractor, duties Duty of engineer. See Engineer, duties. Duty of inspector. See Inspector, duties. Duty of a pump, defined, 135 Dynamite, 296-298, 300-302, 304, 305 cartridge, 268, 296, 302 thawing, 301, 302 Dysentery, 365 Earth pressures, theories, 274, 275 Economical dimensions, mathematics of, 401-403 Effective size of sand, defined, 456 Efficiency of a pump, defined, 135 Effluents, character of activated sludge, 467, 468 chemical precipitation, 408 contact bed, 434 Imhoff tank, 414, 424, 425, 432 lime and electricity, 489 Miles acid process, 484, 485 sand filter, 453 INDEX 519 Effluents, sedimentation tank, 401 septic tank, 412-414 Egg-shaped section, 67, 68, 70 Ejectors, air, 150, 151 Elastic arch analysis, 206-208 Electric motors, 150-152 Electrolytic treatment, 487-489 Elevations, method of recording, 92 Emergencies, duties of engineer, 235 Emerson pump, 261 Engines, internal combustion, 152- 154 steam, types, 142-144. Engineer, absence of, 221 defined, 220 disputes settled by, 220, 234 duties of, 9, 10, 220, 233, 234, 238 individuality and personality, 9, 234 qualifications, 9 sanitary, definition, 2 Engineering News pile formula, 125, 126 Entering sewers, precautions, 335, 336 Enzymes, 365 Equipment for construction, 237 Equivalent sections, defined, 72 solution of problems in, 67-72 Estimates, cost and work done, 10-14 when made, 226 data for, 235 Excavation, depth of open cut, 284 drainage, 252, 262 hand, 242-245, 249 economy, 245 laborer's ability, 243 lay out of tasks, 243 Excavation, hand, opening trench, 243 vs. machine, 245, 249 tools, 242 machine, 244-246 economy, 245 limitations, 246 vs. hand, 245, 249 specifications, 240, 241 Excavating machines, bucket, 246, 255 cableway and trestle, 246, 250- 252 Carson machine, 250, 251 continuous belt, 246 bucket, 246, 247 drag line, 255 Potter machine, 251 steam shovel, 252-254 tower cableway, 252 wheel excavators, 246-250 Excavation, machine, organization, 249 pumping and drainage, 256, 257 quicksand, 256 rock, 263 264 payment for, 230 specifications, 240, 241 trench bottom, 241, 304, 311 Explosions in sewers, 108, 336, 346- 348 causes of, 346 historical, 346 prevention, 108, 348 Explosives. See also Blasting. Explosives, and blasting, 294-304 ammonia compounds, 297 blasting gelatine, 296 contractor's powder, 294 deflagrating, 294 detonating, 294 detonators, 294, 297-300 " Don'ts," 300, 301 dynamite, 296-298, 300-302, 304, 305 fuses and detonators, 297-300 gelatine dynamite, 296 gunpowder, 295 handling, 300-302 nitro-glycerine, 295 nitro - substitution compounds, 295 permissible, 297 quantity, 304, 305 requirements, 294 strength of, 297, 298 T.N.T., 295 types, 294-297 520 INDEX Exponential formulas for flow of water, 54, 55 Extra work, compensation, 227 Facultative bacteria, 363 Farming's run-off formula, 49 Farms, septic tanks for, 416, 417 Farming with sewage. See irrigation. Fats in sewage, 357-359, 366, 367 from Miles acid process, 485-487 Feathers, for splitting rock, 264 Ferrous sulphate, precipitant, 406- 408 Fertilizer from sludge, 470, 495, 497 Fertilizing value of, activated sludge, 470 sewage, 459, 460 Filter press for sludge, 500, 501 Filters. See under name of filter. Filtration, of sewage, 370, 371, 431-459 action in, theory of, 431 cost, 458, 459 Filtros plates, 477, 478 Finances, mathematics of, 157-160 Financing, methods of, 14-17 Flamant's formula, 54, 56 Flies on trickling filters, 438 Flight sewer, 101, 102 Flood, crest velocities, 42, 43 flow computations, 94-98 McMath formula, 94, 96, 97 Rational method, 95-98 Flow, laws of, 52 velocity of, 52, 90, 91 Fluctuations, in rate of sewage flow, 33-38 in quality of sewage, 368-370 Flush tanks, automatic, 109-113 capacity, 111 details, 110, 112 inspection of, 336, 337 payment for, 217 siphon sizes, 111 Flushing, 109-113, 341-343 amount of water needed, 112 methods, 341-343 manhole, 109 sewer, defined, 8 Foaming of Imhoff tanks, 425, 426 Foot valves, 141 Force main, denned, 8 Forms, design of, 322, 323 length of, 319 materials, 321, 322 oiling, 174, 186, 322 specifications, 322 steel, 325, 326 steel lined, 325 support for, 316, 318 time in place, 319 wooden, 323, 324 Formulas, hydraulic, methods for solution, 55-61 for flow of water, 52-55 for rainfall. See Rainfall. for run-off. See Run-off. Foundations, 99, 124-126 Franchises for sewers, 17 Free ammonia, 366, 367, 374, 375, 410 Freezing, catch-basins, 108 concrete, 186, 187 dynamite, 301, 302 Fresh sewage, characteristics, 352- 354 Friction losses. See Head losses. flow in pipe, 51, 52 Fuel, consumption by prime movers, 153 costs, 153 heat value, 150 Fungus growth in sewers, 333 Fuses. See blasting fuses. Ganguillet and Kutter's formula, 52- 65 Gas, chamber in Imhoff tank. See Scum chamber, engines, 152-154 illuminating, explosive, 347 sewer, 335, 336 Gasoline, explosive, 108, 109, 335, 346, 347 engines, 152-154 and oil separator, 109 odors, significance, 335, 353 INDEX 521 Gearing, reduction for turbines, 140, 146 Gelatine dynamite, 296 Glycerol, 366 Gothic section, 67 Governmental control, stream pol- lution, 380, 381 Grade, of sewers. See also Slope. how given, 281-284 selection of, 90 Stakes, 221, 281-283 Gravel, specifications, 172 Grease, in sewers, 99, 108, 333, 345 cutter, 340 ordinance concerning, 345 traps, 99, 108 Gregory's imperviousness formulas, 44, 46 Grit, cloggs sewers, 333 chambers, 127, 397-401 description, 395, 398 design, 397, 398 dimensions, 397, 398 existing, 398-400 outlet arrangements, 400 results, 397 retention period, 397 sludge analyses, 397 units, number of, 400, 401 velocity of flow in, 396-398 quantity and character of, 397 Gooves in concrete, working joints, 319 Ground water in sewers, 38, 39, 85, 87, 256, 352 Gun cotton, 296 Gunpowder, 295 Hazen, theory of sedimentation, 392- 395 dilution formula, 380 Hazen and William's formula, 55, 57 Head loss, in bends, 116 entrance, 115 friction in straight pipe, 51, 52, 115 Hercules powder, 296 Bering, Rudolph, dilution recom- mendations, 380 Hering, Rudolph, introduction of Imhoff tank and hydraulic formulas, 425 Historical resume of sewerage and sewage treatment, 2-5 Hitch, tunnel frame, 286, 287 Holes, drill. See Drill holes. Holidays, work on, 221 Hook for lifting pipe, 304, 306 Horse-power, boiler, 149, 150 of pumps, 144-146 Horse-shoe sewer section, 71 House, connections, record of, 92, 234 drains, 7, 88, 90 sewer, defined, 7 Hydraulic, elements, 65, 69 formulas, 52-55 jump, 73-74 principles, 51, 52, 72, 73 value of settling particles, 393 Hydraulics of , sewers, Chap. IV, 51- 77 circular pipes partly full, 65, 66 equivalent sections, 72 non-uniform flow, 72-77 sections other than circular, 67-72 use of diagrams, 61-65 Hydrocarbon, 367 Hydrogen sulphide, 353, 366, 410 Hydrolytic tank, 427, 428 " Hypo " as a disinfectant, 491 Hyto Turbo blower, 473, 474 Illinois River, self-purification, 374- 376 Imhoff tank, and chlorination, costs, 487 cover, 424 description, 417-419 design, 419^24 digestion chamber, 422 inlet and outlet, 421 operation, 426-427 patent, 418 results, 414, 424, 425, 439, 467 sedimentation chamber, 419-422 scum chamber, 424 slot, 422 522 INDEX Imhoff tank, sludge, 414, 467 sludge pipe, 423, 424 status, 425, 426 and trickling filter, cost, 479 Impeller, for centrifugal pump, 131, 136 Imperviousness, relative, 40, 42, 44- 46, 95-97 Industrial, districts, 32-37 wastes, denned, 7, 352 tannery, 491 Information and instructions for bidders, 213, 215-217 Inlets, street, 93, 94, 99, 104-107 Inspection, contract stipulations, 221-224 during construction, 233, 234 for maintenance, 104, 333-337, 348, 349 Inspector, absence of, 221, 222 duties, 233-234 qualifications, 234 Institutional sewage treatment plants, 416, 417 Intercepting sewer, defined, 7 Intermittents and filter. See Sand filter. Internal combustion engines, 152-154 Inverted siphon, 113-116 Iron, ferrous sulphate, precipitant, 406-408 cast. See cast iron. Irrigation. See also Farming and Sewage farming, area required, 463 Berlin sewage farm, 460, 461 crops, 463, 464 description, 459 fertilizing value of sewage, 460, 470, 495, 498 vs. farming, 459 operation, 461-463 preliminary treatment, 462, 463 preparation for, 461-463 process, 459, 460 sanitary aspects 463 status, 460, 461, theory, 432 in the United States, 461 Jack hammer drill, 264, 265 Jetting method, 21-23 Jet pump, 259, 341, 343 Joints, bituminous, 309-311 in cast-iron pipe, 164 cement, 307, 308 inspection of, 234 lead, 164 mortar, 307 open, 307 poured, 309-311 cement, 309, 311 riveted steel, 195, 196 sulphur and sand, 309 types, for pipe, 307 working, in concrete, 319 Junctions, 99 Kuichling, run-off rules, 46, 47, 49 storm intensity formulas, 50 Kutter's formula, 52-65 Labor, day vs. contract, 211 costs on concrete sewer, 328, 329 Labyrinth packing rings, 136, 137 Lagging, tunnel frames, 287 for forms, 322 Lagooning sludge, 495-497 Laitance, 186, 188 Lakes, self-purification of, 376 Lampe's formula, 54 Lampholes, 99, 104 Lateral sewer, defined, 7 Lawrence Experiment Station, 4 Leaping weir, 118-121, 337 Legal requirements, construction, 224 dilution, 380, 381 in design, 9 Liernur system, 5 Life, organic in sewage, 363, 364 of sewers, 348-351 Lime as a precipitant, 405-408 with electricity, 488, 489 with iron, 406, 407 Line and grade, 281-284 how given, 281-283 Liquefaction of sludge, 411-413, 496, 497 INDEX 523 Liquid chlorine. See also Chlorine, 491 Liquidated damages, 222 Loads on, pipe, 198-202 Mansion's method, 198-202 trench, 199-202 Lock bar pipe, 197 Lock joint pipe, 177 Long loads, 201 Machine excavation. See Excavation. Macroscopic organisms, 363, 368 Main sewer, defined, 7 Maintenance of sewers, Chap. XII, 332-351 catch-basin cleaning, 343, 344 cleaning sewers, 337-343 complaints, 333 cost, 341 entering sewers, 335, 336 flushing, 109-113, 341-343 hand cleaning, 341 inspection, 333-337 organization, 332 protection of sewers, 344, 345 repairs, 337 tools, 338-341 troubles, 333 work involved, 332 Man, shoveling ability, 243 Manholes, 81, 99-104 bottom, 100 cover, 102-103 drop, 101 flushing, 109, 342 location and numbering, 81 payment methods, 217, 218 steps, 100, 103, 104 Manning's formula, 55 Map, preliminary, 17, 79, 80, 82, 83 Marsh -gas, 347, 366, 367, 410, 415 Marston's methods for external loads on buried pipe, 198-202 Materials, for sewers, Chap. VIII, 164-193 measurement of, 236, 237 record of, 237 unit weights, 201, 202 McMath's formula, 47, 48, 94, 95 Meem's theory of earth pressure, 274, 275 Mercaptan, 367 Metabolism, 365 Methane, 347, 366, 367, 410, 415 Methylene blue, 360 Microscopic organisms, 363, 364, 368 Miles acid process, costs, 487 amount of acid, 483 analyses of sludge, 485 description, 482 results, 483-487 sludge, 485 Mineral matter in sewage, 357 Mirror, inspecting device, 334 Money retained by city, 227 Mosquitoes in catch-basins, 108 Motors, electric, 150-152 Municipal, bond, 14, 15 corporations, 15 n, value of in Kutter's formula, 53 New York City, density of population, 29,31 siphons under subway, 114 grease and gasoline trap, 108, 109 aeration of sewage, 377, 470 cleaning sewers, 332 depreciation of sewers, 348-351 Needle beam, 286, 287 Night, soil, 5 work, 221 Nitrates, 355, 356 Nitrites, 355, 356 Nitrifying organisms, 431, 432 Nitrobacter, 431, 432 Nitro explosives, 295, 296 Nitrogen, cycle, 367, 368 organic, 355, 356 Nitro-glycerine, 295 Nitrosomonas, 431, 432 Nomograph, 55, 56 Non-uniform flow, 72-77 Nozzles. See also Trickling filters, coefficients of discharge, 446 types, 445 524 INDEX Numbering, drainage areas, 81, 94 manholes, 81 Nye steam pump, 260, 263 Obstructions to construction, 235 Odor of sewage, 353 Oil in sewage, 108, 344-348 Oiling forms, 174, 186, 322 Olein, 366 Ordinances, for protection of sewers, 344, 345 Organisms in sewage, 363, 364, 368 Organic matter, composition, 366 Organizations for construction, 315, 317, 328 Orders, to whom given, 222 Outfall sewer, denned, 8 Outlets, 99, 122-124, 373 Overflow weir, 118-121 inspection of, 337 Overhead, costs, division of, 10, 237, 238 -track excavators, 246, 250, 251 Oxidation in streams, 373-376 Oxygen, absorption of, 374-377 consumed, 355, 356 demand, 359-361 computation of, 360 bio-chemical, 359-361 Oxygen dissolved exhaustion of, 366 in dilution, 381 solubility, 362 supersaturation, 361 concentration for successful dilu- tion, 377-380 formulas for concentration, 378- 380 significance of in sewage, 359- 362 Oysters, contamination of, 372, 489 Packing rings, labyrinth type, 136, 137 Palmatin, 366 Parasites, 365 Paris sewage farm, 460 Patents. Protection of City by contractor, 224, 225 Pathogenic bacteria, 364 Pavement, replacing, 329 Payment, final on contract, 228 Payments, methods of making, 217, 218 Periscope inspecting device, 334, 335 Permissible explosives, 297 Phenolphthalein indicator, 408 Photographic records, 238 Piles for foundations, 123-126 Pills for cleaning sewers, 338 Pipe, bedding, 230, 304, 328 cast-iron. See under cast iron pipe. design of ring, Chap. IX, 194-210 external loads on, 198-202 joints. See Joints. sewer construction, 304-311 laying, line and grade, 282-284 organization, 311 method of laying, 304, 306, 307 steel, design, 195-197 stresses in, external forces, 194, 202-204 stresses due to internal pressure, 194 stresses in buried pipe, 198-204 stresses in circular ring, 202-204 wood design, 197, 198 Plankton, defined, 363 in sewage, 368 Plans, changes in contract, 222, 223 Plug and feathers for splitting rock, 264 Pneumatic, collection system, 5 concreting, 320, 321 Poling boards, in open cut, 271, 272 in tunnel, 287 Pollution, legal features, 380, 381 Population, density, 28-31 predictions, 24-27 served by sewers in the U. S., 3 sources of information, 27, 28 and quantity of sewage, 31, 32 Potter trench machine, 251 Powder. See Blasting. INDEX 525 Power pump, 132, 133 Precautions in entering sewers, 335, 336 Precipitants, chemical, 405-407 Preliminary, map, 17, 79, 80, 82, 83 work, 9, 17-23 Present worth, 158, 160 Pressing sludge, 500, 501 Priming explosives, 302-304 Private, capital, 17 sewers, 17 Privy, 5 Profile, for brick sewers, 312 sewer, 92 surface, 88 Progress, rate of, 222 reports, 238 Promotion (inception of sewers), 9 Proportioning concrete. See Con- crete proportioning. Proposal (contract), 213, 217-219 Protection of sewers (ordinances), 344, 345 Protein, 366 Puddling, backfill, 330 Pulsometer pump, 260, 261 Pumping, in excavations, 256-263 selection of machinery, 154-156 equipment, cost comparison, 162 station, 128, 142 costs, 156-163 equipment, 127, 128 Pumps, air ejector, 150, 151 capacity, 129, 160-163 capacity of units, 160-163 centrifugal, details, 130, 131, 136- 138 automatic control, 141, 142 characteristics, 138-140 efficiency, 140 for excavation, 262 motors for driving, 150-152 performance, 138-140 protection of, by screens, 386 selection of, 154-156 setting, 140-142 turbine, 130-132, 154 types, 130, 131 Pumps, centrifugal, volute, 130-132, 154 character of load, 129 costs, 156, 157 description of types, 130-134 for construction work, 256-263 diaphragm, 257, 258 direct-acting, 133 duty of, 135, 136 efficiencies, 135, 136 ejector, 134, 150, 151, 259, 341, 343 jet, 259 need for, 127 number of units, 160-163 packing of, 133, 134 piston, 133 speed, 133, 134 plunger, 133 power, 132, 133 reciprocating, 130, 132-135, 154- 156 for excavation, 262 reliability, 127 sizes, 135 steam, 134, 135, 142-146 consumption, 144, 145 vacuum, 259, 262 improvised for trench work, 257 turbine, 130-132, 154 volute, 130-132, 154 Putrescibility, 359, 360 Quantity, of sewage, 24-50, 84-87 variations, 33-38 storm water, 40-50, 94-98 Quicksand, definition, 256 excavation in, 256 safeguards, 235 Quiescent water, self-purification, 374 Racks. See Screens. Rainfall, 17, 40, 41, 50, 96, 97 data, 17 rate, 96, 97 Rangers, 270-274, 276-279 Rankine's theory of earth pressure, 275 526 INDEX Rapid sand filtration of sewage, 458 Rational method of run-off determi- nation, 40, 95-98 Reaeration tank in activated sludge, 473 Receiving well, capacity, 129, 130 Reciprocating pumps. See Pumps, reciprocating. Records, character of, on construc- tion, 238-240 Rectangular sewer section, 67-69 Regulators, 99, 117-121, 337 inspection of, 337 Reinforced concrete sewer design, 209, 210 Reinforcing steel, specifications, 191 placing, 326, 327 Reinsch-Wurl screen, 384 Relative stability numbers, 359 Relief sewer, defined, 7 Repairs to sewers, 337 Report, engineer's preliminary, 10 Reservoir, collecting capacity, 129, 130 Residences, septic tanks for, 416, 417 Residential districts, characteristics, 32-37 Residue on evaporation, 356, 357 Rideal's dilution formula, 379 Ring, design. Chap. IX, 194-210 stresses in circular, 202-204 River pollution, legal features, 380, 381 Rivers, self-purification of, 373-376 Riveted joints, properties, 196 Rock, blasting, 268, 290, 291 definition, 263*' drill, data on, 266, 267 drilling. See also Drilling, by hand, 264 by power, 264-268 rates, 267 excavation. See also Excavation. payment for, 230 measurement of, in place, 235 tunnels, 290, 291 Rods, sewer, 338 Roman ordinance relative to sewers, 2 Roofs.* See Covers. Root cutters, 340 Roots, 333, 340 Row lock bond for bricks, 312 Running water, self -purification, 373- 376 Run-off, computations, 17, 40, 46-50, 94-98 Safeguards during construction, 221, 241 Salt water, dilution in, 376, 377 Sand, effective size, 456 uniformity coefficient, 456 filters, 452^59 action in 431, 432, 452^54 control, 458, 506-510 description, 452 dimensions, 456 distribution systems, 433, 456- , 458 dosing, 454-456 dosing devices, 506-510 materials, 456 operation, 454, 455 preliminary treatment, 455 rate, 455 results, 452, 453 size of sand for, 456 thickness, 456 in winter, 455 Sanitary District of Chicago, dilution factor, 380 specifications, for manhole covers, 101, 102 tunnel cover, 284 tunnel ventilation, 291 Sanitary engineering, 1, 2 Sanitary sewage, defined, 7, 352 Saph and Schoder's formula, 54 Saprophytes, 365 Screed, 316 Screens, 383-391 chlorination and fine screens, costs, 487 coarse, 386, 391 data on fine, 388, 389 design of, 389-391 INDEX 527 Screens, fine, 381, 382, 387-389 fixed, 385, 390 medium, 386 movable, 385, 386, 389-391 moving, 384-386 openings, 386-389 protection to pumps, 127, 141 purpose, 383 results, 386-389 size and performance, 386-389 sizes, 386-391 types, 384-386 sewage treatment by, 371, 381 Screening, vs. sedimentation, 383 purpose, object, 383 Screenings, character of, 386-389 Scum, boards for, septic tanks, 413, 414 Imhoff tanks, 421 chamber in an Imhoff tank, 424 definition, 495 Sediment, velocity of transportation, 396, 397 Sedimentation, 383-405 definition, 383 Hazen's analysis, 392-395 hydraulic values, 393 a method of treatment, 370 object, 383 Peoria Lakes, 376 protection of siphons, 113, 114 results from plain sedimentation 401 theory of, 391-395 transportation of debris, 396 velocity of, 392, 393 vs. screening, 383 velocities, limiting, 396, 397 Sedimentation, basins, arrangement, 394 baffling, 404 cleaning, 404 dimensions, 401-403 inlet and outlet, 404 operation, 411 types, 395 chamber, Imhoff tank, 419-422 Self-purification of lakes, 376 Self-purification of streams, 373-376 Separate sewer systems, 78-80 Septic action, 353, 365-368, 371, 410, 411, 496, 497 results, 412, 413 vs. sedimentation, 411 Septic tank, 411 baffling, 413, 414 capacities of small tanks, 417 for country homes, 416, 417 covers for, 415 definition, 411 design, 413^17 explosions in, 415 results, 412, 413 seeding, 413 sludge storage, 414 small, 416, 417 units, 415 Septic sludge analysis, 414 Septicization. Chap. XVI, 410-430 a method of treatment, 371 the process, 410, 411 results, 412, 413 Settling solids, 357 Sewage and water supply, 32 aeration, 371, 376, 465-479 alkalinity of, 358 analyses, chemical, 355, 369, 467 interpretation of, 356-362 physical, 352-354 average, 352-355 bacteria, 362-365 biolysis of, 366, 367 changes in, rate of discharge of, 33-38 characteristics, 368-370 characteristics of, 352-354 chemical constitutents, 354-356 classification of, 6, 7, 352 collection, 5 color, 352, 353 components and properties, 352 356 decomposition of, 365-367 definition, 6, 7, 352 disposal. See also Sewage treat- ment. 528 INDEX Sewage, disposal, methods, 6, 370, 371 purposes, 370, 371 domestic, 7, 352 farming. See Irrigation, fertilizing value, 459, 460 flow fluctuations, 33-38 ratio of maximum to average, 36, 37, 85 fresh, 352-354 gas, 335, 336, 353 industrial, denned, 7, 352 life in, 363-365, 368 odor, 353 physical, analyses, 352-354 characteristics, 352-354 quality variations, 368-370 quantity. Chap. Ill, 24-50, and 84, 87 and population, 31, 32 of sanitary. 24-40 variations, 33-38 sanitary, defined, 7, 352 septic, 353, 365-368, 371, 410, 411, 496, 497 stability, 359, 360 stale, 353 storm, defined, 7, 352 strong, 355 temperature, 353 turbidity, 353 treatment processes, 370, 371 A. B. C., 4 activated sludge, Chap. XVIII, 465-479 biological, 371 chemical, 371 contact bed, 432-437, 506 costs, 459 dilution. Chap. XIV, 372-382 disinfection, 489-493 electrolytic, 487-489 filtration, 431^59 increase of, 3 irrigation, 431, 459-464 mechanical, 471 Miles acid process, 482-487 purpose of, 6, 370 resume, 6, 370, 371 Sewage, treatment processes, sand filter, 452-458 screening, 383-391 s'edimentation, 391^109, 411 septicization. Chap. XVI, 4 10430 trickling niters, 437-452 weak, 355 and water supplies, 31, 32 Sewerage, definition, 7 demand for, 2 design, 78-98 growth of, 2-4 historical, 2-4 Sewers, ancient, 2, 3 capacity, diagrams, 56-60 cost, 10-14 definitions of various types, 7, 8 depth of, 88 diameter, 58-60, 88-92 flat grades, 73, 109 flight, 101, 102 inspection of, 333-337 life of, 348-351 location of, 80, 81, 94 materials. Chap. VIII, 164-193 medieval, 3 pipe, properties of concrete, 175 design. Chap. IX, 194-210 vitrified clay, properties, 169-171 profile, 89, 92 section of different types, 67-72 separate system, 78, 79, 82, 86, 87 slope, 88-92 storm-water system, 78, 79, 83, 93,94 stresses in, 194, 198-204 Shafts, for tunnels, 284-287 Sheeting, 270-280 alignment, 240, 241 backfilling, 330 box, 272 design, 275-280 driving, 273 length, 273 lumber, 277 moving, 248 poling boards, 271, 272, 287 pulling, 274 INDEX 529 Sheeting, skeleton, 270, 271 stay bracing, 270 steel, 252, 280, 281 thickness, 276-278 types, 270 vertical, 270, 272-274 Wakefield piling, 273 Shellfish contamination, 372, 489 Shields, tunnel, 288-290 Short loads on trenches, 202 Shovels, for hand excavation, 242 steam. See Steam shovels. Shovel vane screen, 384 Shoveling by hand, height raised, 244 performance by one man, 243 Simbiosis, definition, 363 example, 432 Sinking fund, 158 Siphons, automatic. Chap. XXI, 506-512. See also under Dosing devices. in flush-tanks, 109-110 inspection, 337 operation, 109-110, 506-512 for trickling filter, 448-451 true and inverted, 113-117 Skeleton sheeting, 270, 271 Slope, of sewers, 88-92 of tank bottoms, Imhoff, 419, 423 sedimentation tank, 404 Skewback, 204 Sludge. Chap. XX, 495-505 activated. Chap. XVIII, 465- 479. See also under Activated sludge. analyses, 414, 467, 468, 485, 496 characteristics, 495 definition, 495 digestion tanks, 427-430, 497 disposal methods, 495 drying, 497-505 acid flotation, 503 beds, 498, 500 centrifuge, 501-502 heat, 502, 503 press, 500-501 thickeners, 504, 505 fertilizing value, 470, 495, 497 Sludge, filters, 498-500 lagooning, 495, 496 measurement, 427 press, 500, 501 sedimentation, 401 septic analysis, 434 treatment methods, 495 Soaps, 357 Soil, bearing value, 125 stack, definition, 7 Solids in sewage, 356-368 Special assessment, 15, 16 Specifications. Chap. X, 211-232 general, 219-229 special, 230 technical, 229, 230 Spiling. See Piles. Spirillum, 362 Spores, 363 Springing line, 204 Sprinkling filter. See Trickling filter Square sewer section, 68, 69 Stability, relative, 359-361 Stagnant water, 374 Stakes, contractor to provide, 221 where driven, 281, 282 Stationing, 92 Stay bracing, 270 Steam boilers, 147-150 Steam, consumption by, pumps, 144 145 turbines, 144, 147 engines, 144, 145 pumping engines, 142-146 pumps. See Pumps, steam. shovels, 246, 252-254 turbines, 146, 147 Stearin, 366 Steel, forms. See Forms, steel. pipe, 164, 191, 192 design, 195-197 specifications, 191 reinforcement for concrete, 191, 326-327 sheet piling, 252, 280, 281 Stench, historic in London, 4 Sterilization. See Disinfection. Storm, sewage, definition, 7, 352 530 INDEX Storm, sewer system design, 93-98 water, quantity, 40-50 Storms, extent and intensity, 50 Stream pollution, regulation, 380, 381 Streams, self-purification, 373-376 Street, inlet. See Inlets. wash, definition, 352 Stresses, in buried pipe, 198-204 in circular ring, 194, 202-204 Sub-main, defined, 7 Subsurface surveys, 18-20 Suction for centrifugal pump, 141 Sulphur and sand joint compound, 309 Sunday work, 221 Surface, elevation, 92 of ground, character, 44-46 profile, 88 water, 7, 352 Surveys, underground, 18-20 Suspended matter, 357 Talbot's run-off formula, 49 Tamping, backfilling, 328-331 Tannery wastes, disinfection, 491 Taxation, general, 16, 17 Taylor nozzles, 444, 445 Temperature of sewage, 353 Templates, brick sewers, 312 Thawing dynamite, 301, 302 Tide gate, 122 Timbering tunnels, 286-288 Timber, strength of, 277 Time of concentration, 41-43, 95- 97 Tools, for cleaning sewers, 337-341 excavating, 242, 246 Tower cableways, 252 Trade wastes. See Industrial wastes Traps, in catch-basins, 107 grease, gasoline, and oil, 108, 109 in street inlets, 104, 105 Travis tank, 427, 428 Tremie, 187, 188 Tree roots, 333, 340 Trench, backfilling, 328-331 blasting in, 244, 269 Trench, bottom, shape of, 241, 304, 311 breaking surface, 243, 244 drainage, 256-263 excavating, by hand, 242-245 machine, 244-256 guarding and lighting, 221 layout of tasks, 243 length of open, 241, 248 line and grade, 281-284 location, 243, 281 opening, 243, 244 pumps, 256-263 sheeting, 270-280 width, 240, 241, 246 Trestle excavators, 250, 251 Trickling filter, 437-452 advantages, 438, 439 covers for, 451 depth, 441, 442 description, 437, 438 dimensions, 442 distribution of sewage, 442-451 dosing siphon, 446-451 dosing tank, 446-451 head lost, 438 insects, 438 material, 441 nozzles, 442-451 layout, 447-451 odors, 438, 439 operation, 441 rate, 441 results, 439, 440 siphon size, 449-451 underdrainage, 451, 452 unloading, 431, 437 Tripod drill, 265 Triton, 295 Troubles with sewers, causes, 333 Trumpet arch, 121 Trunk sewer, defined, 7 Tunnels, 283-294 backfilling, 331 breast boards, 288 brick invert, 313 compressed air in, 292-294 concrete construction, 320, 321 depth of cover, 284 INDEX 531 Tunnels, line and grade in, 283 machines, 290 rock, 290-292 shafts, 284-286 shield, 288-290 timbering, 284-288 ventilation, 291, 292 Turbidity of sewage, 353 Turbine, for cleaning sewers, 340 pumps, 130, 132 steam, 146, 147 Typhoid fever, 364 U-shaped sewer section, 67, 69, 71 Underdrains for. sewers, 126 trickling filters, 451, 452 Underground surveys, 18-20 Unexpected situations, 235 Uniformity coefficient of sand, 456 Unloading of filters, 431, 437 Urea, 367 Valuation of sewers, 332, 348-351 Velocities, depositing, 395-397 distribution of, 51 flow in sewers, 90 over surface of ground, 42 limiting for sedimentation, 396, 397 limiting in sewers, 396, 397 principles of flow in sewers, 51 transporting, 396 , Ventilation, air pressures, 291 compressed air, 292-294 pipes, 291 Ventilation, of sewers, 102, 103, 335 tunnel, 291 Vertical sheeting, 270-274 Vitrified clay. See Clay vitrified. Volatile matter in sewage, 357 Volute pumps, 130, 132, 154 Vouissoir arch analysis, 204 Wakefield piling, 273 Wales, 288 Waste pipe, defined, 7 Wastes. See Industrial wastes. Water consumption, 31-33 flow of, 51-77 rate of steam engines, 144, 145 supply and sewage flow, 31-33 Watershed. See Drainage area. Weight, of backfill, 199 of building material, 201 of moving loads, 200, 202 Well, hole, 101 points, 262, 263 Wheel excavator, 246-250 \V^ing screen, 384 Wood, forms. See Forms. pipe, materials, 164, 165, 190, 192 193 design, 197, 198 working strength of, 277 Work, extra, 227 preliminary to design, 9 Sunday, night, and holiday, 221 Workmen, competent, 227 dishonesty, 233, 234 RETURN TO the circulation desk of any University of California Library or to the NORTHERN REGIONAL LIBRARY FACILITY Bldg. 400, Richmond Field Station University of California Richmond, CA 94804-4698 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS 2- month loans may be renewed by calling (510)642-6753 1-year loans may be recharged by bringing books to NRLF Renewals and recharges may be made 4 days prior to due date DUE AS STAMPED BELOW OCT 2 9 1996 AUG 2 9 2003 20,000 (4/94) UNIVERSITY OF CALIFORNIA LIBRARY